Yep. There are three very good reasons for using groups in echo.
Creating a Control Group so you can use a generic command
First, you can create a “smart home devices group” By adding one Alexa device to that group. For example, if you have a dot in the living room, You can add just the lights in the living room plus that dot to one group. And if you have a show in the kitchen, you can add just the lights in the kitchen plus that show to a different group.
At our house, We name these “{room} control group” so we know that group was created only for the purpose of allowing that echo device to control those specific lights.
After that, if you are standing in the living room and just say “Alexa, turn on the lights“ just the lights in that particular group will come on. But if you were standing in the kitchen and said “Alexa, turn on the lights,” only the lights in the kitchen control group would come on. Notice I said the same thing each time, but the Alexa each room was smart enough to know I only meant the lights in that room.
This has been great for visitors, because anyone can walk into any room and say “Alexa, turn on the lights” and only the lights assigned to that echo device’s control group come on. Much simpler than having to teach other people the names of the different devices – – or even the names of the rooms.
Amazon calls these a “smart home devices group.“ At the present, you can only include certain kind of switches and lights, but you cannot include a thermostat, for example. But it is still very convenient.
And of course with SmartThings, you could include a virtual switch in the group, and then have that virtual switch coming on trigger anything that smartthings Can do. 
Accommodating Synonyms
At our house, we are three housemates. We have one small room with bookcases, a desk, and a reading chair and not much else.
One of us calls that “the office,” One of us calls it “the study,“ and one of us calls it “the den.” When we are just talking among ourselves, it doesn’t matter – – we all know which room we mean. 
So in Alexa so we set up three different groups (One called “office”, one called “study” and one called “den” with the same devices in each group.) so the voice commands work for everybody, even though we are each using different commands.
using groups to create functional zones
We also use groups to create functional zones so we can turn a set of devices on or off together for particular kinds of activities. For example, I have a group called “bedtime“ which has just one light from the living room, one light from the hallway, and one light from my bedroom. So when I am ready to go to bed, I can turn off the Living room lights, but turn on this pathway of lights so I can see my way as I go to my room.
We might have another group called “downstairs” which has all the lights from the downstairs area Except for one light Near the entryway which we leave on.
We might have another group called “bedroom main lights” which turns off all the lights in the bedroom except for one nightlight.
And we might have still a different group called “Milo” (Named for Milo the dog) which turns on one light in the bedroom, one light in the hallway, and the yard light. Used when we want to let the dog out late at night.
And there might be one single device, a table lamp in the bedroom, that was in all of these groups.
So sometimes you group by activity rather than by location. 
Amazon’s implementation of groups for Echo is very flexible, and can be used in many different ways.