It's there for exactly the same reason
to force players to chose which resources to take into battle
This is wrong. I can see it for something like say, health potions. Each character's only got so many spaces they can stow a potion bottle without bordering on "portable hole" territory. Or even party members - some reason why I shouldn't just take along -everyone- and have to leave some behind.
But abilities? Let's say my character has a shield sustained that makes him immune to knockdown, similar to DAO. Now I don't want to map it all the time, because I don't get much trouble - but if an ogre, or a giant, or a damned dragon shows up - I'll want to use it. Guess what? I either have to have foreknowledge of an encounter, save scum, or be totally unable to use it at all.
This is not good design in any stretch of the imagination.