When checking the status of my various colonies, I'll often run through the various tabs to look for issues, etc. When it comes to ground units, however, the only way to see exactly what is on the colony is to open the Ground Forces window.
I think the GU Training tab has plenty of room to add a list of ground units that are in the colony, so it could become the "Ground Forces" tab.
The Order of Battle tab on the Ground Forces window is still very useful, so I wouldn't want that to go, but it sure would be handy to not have to go to it just to find out if I've left my xeno team or my geo team on a random colony that I'm looking at.