Ah I see.
I agree with iStealtherl. Good feature - just needs a good UI to match.
Suggest grouping all assigned units in the Units Deployed section by assigned group numbers, making it easy to see what's in which group.
Also, suggest making groupings mandatory, for uniformity's sake. When a unit is selected and given a separate order, automatically assign to either a separate group (any unused group number), or into a special temporary group (a detachment) with appropriate hotkey. (you could use combination hotkeys for this - 1 for group 1, and 1-1 for detachment 1 of group 1)
Will elaborate further if the devs want. (Do set up a suggestions thread for things like these)