That’s a pretty hard question to answer, and it depends on how the group is used.
But one way of verifying this is to check when any of it’s members logged on last time. There is an obvious risk that the group is not used for anything in particular but it still might have users/computers in it, but it might give you a hint.
I therefor wrote an advanced function that can help you with this.
It’s pretty straight forward to use, just write:
Get-ADGroupLastUsed -Identity "Domain Admins" -Recursive
The “Recursive”-switch makes it resolve the members in all child groups. It works for both user and computer objects.
This can be pretty useful in certain scenarios, and I hope it might be of use for you too!
The code is available at this link.