spoilers xDQuote:
Item Manager is a stupid way to be able to bypass the game's equip check.
That being said, all it does is save the ItemUID's of the items inside the slots and restores them later. You can skip this step entirely, which is what I did in my ITC.
It used to be much more useful back when items were by the hour, so you could essentially use an item forever without really wearing it. It still can be used for durability though, say you have an unlimited item and don't want the durability to go down, you'd use this. But then in your info it'd show that you weren't wearing said item - therefore pointless unless you hide your info. :p
Just my two cents, felt like typing something on my new keyboard. <3