I have a door and a handle that share the same UV. The handle is attached to the door so they become one object, but not a seamless mesh. As a result they cannot be stitched in the UV, so they are separated if I attempt to pack them. Grouping them in the UV didn’t seem to make a difference.
I was able to fit the elements in the map without the help of packing, but I’d still like to know if there was another way (they actually had to be separate in this case, but what if it was a different case?)