So it basically just cleans up your inventory?

So it does nothing...

It supposedly can be used in a glitch to transfer items between characters, so you could give a high level weapon to a low level character

do you lose the items in bottomless box if you go ng+?

Lmao the grammar

There is an inventory weight that when full, causes your character to not be able to pick up items. I bought a lot of giants shield's to do a glitch I later relisted was patched. If you store said items in the bottomless box, it does not allow you to hold more items. My inventory is now functionally clogged and I can't pick up weapons.

"Some deride it as a symbol of unbridled avarice." This wording sounds an awful lot like the Symbol of Avarice item ingame, which is basically a mimic head. There clearly is a connection between this box and mimics. Don't feed it too much, or you might regret it...

Hypothetically, How big is the box compared to the character?