It's important to remember the difference in behaviour of the grouping tool when used in the Setup room and the Pose room.

When used in the Setup room you are working on the figure as a whole and can move polygons between body parts (breaking any morphs) and probably creating unwelded segements.

When used in the Pose room you can only work on one existing group to create subgroups which is useful for changing material assignments or limiting the affect of a magnet.