Fallout's time limit is pretty much the simplest thing in the world, yet it still solves many of the most common problems that are related to cRPGs. It heavily discourages certain behavior that usually would be easy to abuse, like resting after every battle to regain full health, or making several trips to a vendor in order to be able to sell every item you find in the game world. It actually gives you a reason for doing side quests, as spending some additional time at a single location exhausting every possible lead is preferable to blindly heading out into the desert and possibly wasting weeks of valuable time wandering around aimlessly. It also makes it important to actually keep your focus on the main quest, unlike so many other games where you're told to hurry but will more likely spend most of your time running errands to other people and saving the actual super important quests for dead last. The time limit also adds another layer of decision-making into the game, as poor choices may lead to an actual game over, which is of course utilized very well with the water merchants, for instance.
Admittedly a poorly thought-out time limit could potentially even ruin a game, but when it's done correctly (meaning that it's lenient enough that you can take your time with the game, but not too lenient to make itself pointless), it can really make a game better. The Spirit Meter is good for some of the same reasons, although it's of course a very different and more complex mechanic.