In halo 3 you had the bungie body which gave you flames and the katana chest piece which gave you a sword on your back. Now this isn’t a huge deal in this game but what if you wanted a different chest piece when using one of these things or wanted to use both together? Again in this particular game it isn’t a huge deal due to the bungie body being only available to the community for one day and they now have an armor effect section for things like the flaming helmet, but if you wanted the katana sword with out being stuck with the hayabusa chest you couldn’t do anything.
In Reach you have kat’s robotic arm stuck with a particular few chest pieces, so if you want her arm you may have to choose a piece of armor you may not want, same goes for Emile’s grenade belt.
So i purpose a “attachments” section in the armory for halo 4 for things along these lines so you aren’t forced to a certain chest piece for them, also if they don’t conflict such as all the above they should be able to be put on at the same time.