While I do think encumbrance in a Bethesda game is pretty pointless I do believe it serves a purpose in BG3. Barrels full of all sorts of liquids are extremely useful, their drawback is that they weigh a ton. Encumbrance exists to prevent you from being a barrelmancer. I think you can also pick up any chests, so you can just carry away all the chests you can’t unlock and then break them somewhere safe (or move them to you lockpicking character etc).