This is one of those areas where I definitely want to effect a change, but the manner for doing so is slightly unwieldy. Let’s define the terms. Weight is simply how heavy an object is. Encumbrance describes how restricted you are by a combination of an object’s weight, its fragility, and the ease with which it is carried.
A small metal vial containing poison antidote might weigh about half a pound. In BG, there are no fractions. This potion has to be either weightless or twice as heavy. Its encumbrance is almost negligible. These facts combine to make this potion more encumbering than it should be, a due paid for its translation into a computer game.
At the other end, we have a suit of plate mail: large, heavy pieces of thick metal. It is exponentially more encumbering to carry than to wear, but there is no way to represent that in BG.
Then we have BG’s inventory system. On one hand, it wants to be realistic: STR-determined carry limits, a finite number of slots for equipped items, and a finite number of slots for carried/unworn items. For convenience, they also allowed for the stacking of certain items — ammuntion for missile weapons, scrolls, and potions mostly. Unfortunately, the limitation of the engine once again makes something inconsistent, and both unrealistic and inconvenient. You can stack arrows, but only arrows of the same type. You can stack spell scrolls, but only of the same spell. Unique scrolls, such as quest clues or notes, can’t be stacked at all. Then they added in portable containers, where like-item-stacking was not a concern, but also completely obliterated the point of limited carrying capacity in the first place. In other words, it’s an incoherent mess that serves no purpose other than to clumsily and impotently limit what and how much a character can carry.
There are very good reasons for wanting to limit how much a character can carry. You don’t want them to be able to horde potions and spell scrolls, saving them for the otherwise really tough encounters, by deliberately not using them for the numerous token battles. But inventory restriction is the wrong place to address this. The encounters should be designed to need those assets more often, and they should be harder to come by.
On the other hand, in P&P, players would have the option to hire porters and henchmen, hirelings that wouldn’t necessarily affect the outcome of an encounter, but would allow the party to lug around much more loot and equipment. As it is in BG, one of the biggest restrictions on this — the weight of coinage — isn’t even an issue.
I’m not quite sure why I would restrict inventory, even if I can figure out how, but I do know I don’t like the idea of a character carrying multiple suits of armor, or an entire collection of weapons like a portable armory.