Ashley For me it's just organizational thing using more than one Box2D world. I can setup character on one Box2D, and assets that needs to explode all over the place on another. So most changes I am doing is on Box2D itself without need to tweak each asset that belongs to different group/family, and as a benefit, those Box2D worlds don't collide.
Speaking of collision, I currently have more than 30 pieces that are not suppose to collide physically. The fastest way I figure out how to do this is: put all 30 pieces in one family, in event editor select each peace and switching off physics collision with this family. However, that's 30 actions, and family doesn't hold physical collision action, is there any faster way to do this?