When a model has repeated parts, it would be really nice to be able to make "instances" of a part. An "instance" would have its own 3D transform (including scale, I suppose) able to be applied, but any changes to the original group—e.g. entering the group and resizing a particular hole—would affect all instances. Ideally you could enter/edit from any instance and it would be the same as editing the original group.
I have different GoPro rigs that use the same complex "frame" shape to hold each camera, rotated and transformed at odd angles and unique positions. When I realize that I need to adjust the frame (e.g. make the main hole a little tighter, give more room for a notch over there), I have to either enter each frame group and do the same work (often changing the workplane to account for custom rotations), or I have to delete all but one frame, modify the original, and then copy it many times and try to get the transforms right again. Done once, this is obnoxious but not terrible. Done 10 times, it's pretty terrible.