Certain pieces of equipment, mostly level 1 cosmetic-only items, are considered part of a set.

the most obvious of these are the ones you can grab out of a coffer, like the 2B costume

or perhaps something even more obvious, the Emperor's New Equipment, which covers every slot.

The Emperor's new Equipment gloves, hat, pants, etc. each take up a slot in your glamour chest, and if you have all 9 in there, you've lost quite a bit of real-estate

the new system allows you to compress the amount of slots taken in your chest, allowing you total access to all 9 glam pieces for just one slot in the chest, letting you cram even more into it

However, there are caveats

1: You have to have the entire set on hand to do it.

No incomplete sets, it's all or nothing, and if you've been cherry picking these items off the market board, getting the rest can get real expensive real quick

2: You can't do the compression if they're already in the glamour chest

Armoury chest or inventory, they have to be on your person, and you'll have to click the icon by the set-piece you want to compress to begin the process

remember caveat one during this

3: they may only take a single slot of space in the glamour chest, but it's still one prism per item

keep track of your prisms, especially if you have to retract items from the chest that you've already glamoured.

that's it, thank you for coming to my ted talk