Interesting stuff!
As you may know, this forum is specifically for users of the Samsung SmartThings ™ Home automation platform, and one of the advantages of that platform relative to its competitors is its ability to support very complex rules.
How to Get Started Creating Complex Rules in SmartThings (2017) (SmartThings Classic)
Two of the most popular complex rule categories have to do with an “unless“ condition. 
- For example, turn on the Living room light every night at 15 minutes before sunset unless The television in the living room is already on.
Or
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If motion is detected by the front door, turn on the porch light and turn it off again after 15 minutes of inactivity unless the porch light was already turned on by the wall switch, in which case just leave it on. (this one is also called an override condition.)
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Another one that comes up a lot, (in particular because the V2 classic version of the smartthings app allowed for it and the new V3 version does not yet) Has to do with putting the same mode/condition on both sides of the IF statement.
This is commonly used with a virtual switch which is acting as a proxy for another condition, but there are other use cases as well. Or if you are changing the location.mode.
For example “if the location.mode is “away“ and Charlie arrives home, change the location.mode to “Home.”” You would use this when there are multiple location.modes and you don’t always want to switch the Mode to home when Charlie arrives. For example, families that have a “guest” mode for when A friend is visiting might have the system in “guest.home” mode. They don’t want that to change just because Charlie comes home.
Or “if switch A turns on, Turn on the pump switch and turn switch A off again.”
In this case, I think the inability to do this in the new V3 app is probably a bug and hopefully that ability will be added again soon.