I'd like to talk about the purpose of weight capacity in a game, beyond just the simple reduction to "it's more realistic." Some games give you all of the numbers: weight of each object, how much you can carry, and how much you're currently carrying. Some games (modern FPSs mostly) restrict purely the number of items you can carry regardless of how much they might 'weigh'. Still, other games eschew this entirely (e.g. many JRPGs) and allow you to carry 99 Tents and 99 Cabins and 99 Great Big Swords as well as whatever else.
I find myself wondering what in-game functions are supported by restricting how much a character can carry.
The less you can carry, the less you can bring home to sell from a long haul. Diablo is well known for this (though really it just forces repeated laps to and from town) but even a game like Fallout sees the same restriction (and the lack of teleportation/quick travel makes the limitation even more tangible). This puts a cap on the amount of resources a player can gain from an expedition, as it were; you may need to make choices on what to bring to town to sell and what to leave behind, perhaps not knowing which is more valuable.
Carrying capacity also restricts your flexibility; this is its primary use case in modern FPSs (which allow you typically a primary weapon, a sidearm, and some kind of utility item) but it comes up in other games as well; while it might be nice to have two kinds of rocket launchers, a grenade launcher, a flame thrower, two kinds of chainguns, and several rifles - something for every occasion - you just can't carry them all. This very often meshes with the previous effect: you now need to budget carrying capacity between:
- your ability to address different situations with the ideal weapon;
- and your ability to carry more junk to sell for money.
Fallout 3 (and New Vegas unless you kicked in Hardcore mode) ignored the weight of ammunition and 'chems' (stimpacks for healing and other things that granted buffs) but its predecessors did not; stim packs were light (and expensive), but first aid kits and doctor bags were heavy, adding your ability to address character injury to the 'what do I carry' budgeting.
Items are resources (either they serve an intrinsic function or they can be sold for currency or maybe broken down and used to build things that serve one of those two purposes) which ultimately assist the player accomplish tasks; restricting how many you can have puts a limit on your resources. Additionally, it does add a touch of realism to the game. ;)
Does it have any other effect that I'm missing? What do you think?