Recently a friend shared a story where he tried to explain 3.5 after playing 4e for awhile. I don’t remember the exact quote, but he was describing how armor weight interplays with other gear weight (in non-linear fashion) when determining encumbrance for determining armor check penalty and speed penalties. Encumbrance is something I’ve generally always played without. My house rule is generally: everything can fit into the backpack, but nothing unusually large or heavy (doors, statuary, ladders, bodies, etc).
The advantage of an abstracted inventory is that it takes away tedious bookkeeping. Also by having a vast arsenal of items on hand, it makes it possible to MacGuyver up some interesting solutions to puzzles and other situations. The downside is that it takes away some of the challenge and a lot of the realism. But D&D is supposed to be heroic, not realistic… so I guess that’s kinda moot.
Besides the size and weight there’s also an issue of location. Obviously the equipped items are filling up some slot on the body, but everything else? Is it in a belt pouch, pockets, backpack, saddlebags, chest strapped to the pack horse? Normally an item’s location doesn’t make a difference; it’s always just a minor action away from my character’s hands.
But what about if an enemy wants to steal or attack an item? Called shots, sundering, and pickepocketing are out of the rules in 4e so I guess it’s pretty much at DM’s discretion. This is good for an enterprising player that wants to lift a key out of a guard’s pocket, but bad if the DM turns around and has an enemy ritual your sword right out of your hand!
To that end, even though I don’t fastidiously record the weights and locations of everything, I like to have a general sketch of where all my character’s items are, even if there is probably more than is reasonable in the backpack. That way if my DM is feeling evil, I can at least make a case for saying something is hard for an opponent to get at.