While watching the ArmA 3 Livestream - Launch Sneak Preview I couldn't help but watching Zipper unassigning (group) every module he created. This is something that was in ArmA 2 as well, and has little to no use in general.
As far as I can remember, modules are the only non-"playable unit" that gets grouped. Triggers and empty vehicles does not group automatically.
Source: http://youtu.be/PqQewm7T3EM?t=27m27s