Actually it makes sense.

I'm doing crowds. And i don't want to populate the whole scene and save it with 100 characters . impossible. 

But with saving groups of 2, i can then load crowd groups of 2 into my scene to set them up in relation to the ground and camera( camera angles etc) . Then i can make A transparent movie with only the 2 crowds for use in Final cut .. THEN i can put the crowd group as a layer either in front of the character or behind it. You see, there's a point to what i'm doing.

Also by grouping them i can put 2 together. instead of having to position one character, cloth him.. Then load another one and try to find where the other one is so i can put him next to it.

Grouping characters and saving them to the libraries is useful.