I have some questions about Lighting Groups in the new app.
Are Lighting Groups controllable by Automations? If so, how?
Among other differences, a Lighting Group can be turned on and off where as a Scene can only do one or the other. Is that correct?
Can a Lighting Group be used by Alexa? If so, how?
Not yet
Correct
Not at this time
See this thread:
Searched for this topic before creating a new one, I would also like to known when âLighting Groupsâ will be available in automation. Is there a more specific date than âSoonâ?
Short answer: No. 
However, for some purposes, such as turning on several lights at the same time, a scene might work, and scenes can be used in automations. But youâd have to have one scene for on and one for off. So not as good as real groups, obviously.
The other approach is what we used to do with the classic app. Create a virtual device to stand in as a proxy for the group. Then have all of the individual lights âmirrorâ the proxy. (Of course, that requires one SmartLights automation for each of the lights in the group, which is a lot of work to set up.) Now you can put the proxy into automations and the individual lights will all follow its state for on, off, and Dimming. But it doesnât work for color temperature.
So it all depends on what you were trying to do. I agree that itâs very odd that this doesnât already exist in SmartThings. 
Thanks for the answer, very strange to create a very much wanted grouping tool then not allowing anyone to utilize it in automatons or scenes? Never mind, hopefully an update in the app soon enough!
Is this still not available?
I want to automate my light groups! 
Nope, still canât control them as a group. Your best options currently are using scenes or the community created SmartApp Trend Setter. With TS, you create a virtual device that acts as a lighting group and can control all devices in the group, including the dimmer, temp and color. The benefit of this over a scene is that, as @JDRoberts stated, youâll need a scene for on and a scene for off. And multiple scenes for different dimming/temp/color.
While lighting groups are not available in ST, they ARE available in Amazonâs Alexa app which integrates with smartthings and acts as a controlling front-end for ST so Iâd recommend you install the Alexa app for this use case. Of course the Alexa app will provide plenty of other ST features such as voice control, new ways to design if>then commands, etc, and you donât even need to own an Alexa device!
The problem with using virtual switches to control groups of lights is that they remember their âstateâ. i.e. if you turn all your lights on with the virtual switch and have your physical switches mirror this, it will work great. But then if you use your physical or any other kind of command to turn the lights off individually, the next time you tell ST to turn on the virtual switch it will do nothing because within ST the switch is already on; as it was never turned off. Using the Alexa lighting groups solves this.
One other tip for Alexa is it may not be compatible with all of your ST devices so you might have to create virtual switches in ST that ARE compatible w/ Alexa, and then have that virtual switch mirror the behavior of the incompatible switch as a workaround. Virtual switches can be used this way to pull almost any other ST action into the Alexa front end as well. For example if you want your Alexa devices to say âAlarm disarmedâ every time you disarm you ST alarm, you can create a virtual switch called Tell_Alexa_Alarm_Disarmed and have ST turn this switch on and off every time your alarm is disarmed. You then tell the Alexa app to speak every time that switch is turned on and voila.
You are replying to a post which is two years old, and a lot has changed in that time, so people may feel a little confused. 
As far as specificsâŚ
While lighting groups are not available in ST,
As of this writing, smartthings does offer lighting groups, itâs just that you canât do anything with them except activate them through the smartthings app. You canât include them in scenes or routines and they are not visible to the voice assistants.
they ARE available in Amazonâs Alexa app which integrates with smartthings and acts as a controlling front-end for ST so Iâd recommend you install the Alexa app for this use case. Of course the Alexa app will provide plenty of other ST features such as voice control, new ways to design if>then commands, etc, and you donât even need to own an Alexa device
The smartthings integration with Alexa is complicated. Alexaâs groups are great, but they are NOT available for use in SmartThings routines. You can use them in an Alexa routine, but then you are back to needing a virtual device to trigger that routine from SmartThings. So great for voice control of a group, but otherwise does not meet the OPâs requirements. (At the time the original post was written, âautomationsâ was the term used for what are now called âroutinesâ in the smartthings app. So that was a very specific question not related to voice control.)
The problem with using virtual switches to control groups of lights is that they remember their âstateâ. i.e. if you turn all your lights on with the virtual switch and have your physical switches mirror this, it will work great. But then if you use your physical or any other kind of command to turn the lights off individually, the next time you tell ST to turn on the virtual switch it will do nothing because within ST the switch is already on; as it was never turned off.
SmartThings has always offered several different types of virtual devices. There are both virtual binary switches, which are on/off devices, and virtual momentary switches, which are more like a doorbell button. You turn it on and then it immediately turns itself off again. Its resting state is neutral. So the issue you raised will not be a problem as long as you use the right kind of virtual device. 
It is definitely strange that two years later smartthings lighting groups still are not actionable except in the app itself and still donât work with the voice assistants, but there we are.
It is definitely strange that two years later smartthings lighting groups still are not actionable except in the app itself and still donât work with the voice assistants, but there we are.
Was just thinking this exact thing while iâm updating Rules in the API for this exact purpose. Such a simple and common concept that weâve waited years for a better solution for and yet, here we are (as you said).
ST are way too slow to implement changes. Listen to your community Samsung! I reported in July 2021 the scene button under Favorites is too damn smallâŚcanât really display enough info to know what it does. No changes! Zero
Yes that is infuriating. All my scene tiles are identical. I need to see the end of the label, not the beginning, though obviously all of it is better. I just donât get why they canât be the same width as Routines.
Two years later and here we still are 
This thread was the top Google search result when I did a search after noticing âLighting groupsâ, adding one, and then realizing I canât control it from an Automation.
Like others I was trying to clean up the huge number of scenes I have (one for ON, another for OFF) with labels that are truncated in the UI.
Guess Iâll be patient 
You canât use Lighting Groups in app Routines or Scenes but you can certainly turn them on and off using other automations that use Rules or the API. They are just devices.
Iâm trying to keep my setup simple, using built-in features that (hopefully) SmartThings wonât take away without providing a seamless migration path. Obviously that excludes the API since Iâm not a programmer, but Iâll look into Rules.
This evening I just used Lighting Groups in an automation. I discovered they worked as I was cleaning up some old SmartLighting rules and had originally tested by creating scenes (per above, one for on and one for off). The Lighting Group essentially behaves as a device, it shows up in a room, and I used it to turn on and turn off all of the switches in the group through a single instruction in the automation. Nice.
The only advantage over a Scene is you can turn it on/off eliminating the need for a different Scene to change state from the previous one. They donât run local even if all the devices in the group have Edge drivers. Better off using an Edge virtual switch to control a group of devices via a Routine so the Routine runs locally.
Yes, that makes sense. In my case, some of my switches are Kasa plugs, and so cloud based anyway. Grouping them together is a tidy way to do that for me.
Sure, if youâre already having to rely on cloud to cloud, then this is a reasonable way to manage multiple lighting devices.