An excellent feature would be to be able to group a series of objects in forge, that are already assimilated, and be able to move them in unison to another location, or merely copy them- while being able to move/rotate their position.
For an example I built an interesting map in Halo 3- Sandbox, inside the crypt- however, after completing it, I realized it would be far better served to be in the skybox. Spending the hours upon hours though to recreate the map would be terrible- being able to simply move it would solve all my problems, and it doesnt seem like that would be too difficult to program.