Resting also gives you a chance to interact with your party members, maybe craft, maybe scribe scrolls, maybe alchemicalize some potions and it will definitely be used to progress party member romances and quests. Requiring rest for spells and abilities instead of just making it gameplay pointless means you get to experience these things no matter your playstyle.
This is a fantastic point. Even if on the bottom line it feels pointless, it gives you an opportunity to see all of these interactions on a regular basis and consider these things. Considering that, I wouldn't have it any other way either.
As for saving spells for what's ahead, that's what I was sort of trying to get at. Simply backtracking to rest looks easy enough. You make a good point in "sudden encounters", though. If there's another, unexpected fight right after another one, there is no chance to rest. Having that happen quite often would be a pretty major hassle, though...
