As I see it, self-imposed restrictions on gameplay are always worse than having the game impose real restrictions. But they can be worse in different degrees.
roshan mentioned playing Fallout 2 in ironman mode as an example. The main issue of doing that is that Fallout 2 isn't really designed with ironman in mind, and repeating the beginning of the game several times can be really annoying. Rogue-likes, on the other hand, don't suffer from this problem because they are built around this kind of gameplay, usually having several random elements that assure the game won't become repetitive while the player is still learning the ropes.
However, ironmanning is one of the best self-restrictions one can use in these games, because it is pretty clear when you would be breaking it (whenever you reload to a point before something happened, possibly with the exception of bugs). The rest thing is not so clear, however. Of course, if you are resting between every two fights, you are doing it wrong (though those early levels can be a bit problematic). But without the game enforcing any kind of real restriction, it doesn't feel much fun, because you don't have any kind of standard to meet but your own. Maybe you can make your own rules, such "at least three fights before a rest", though these feel arbitrary. You can try to beat your own best (in game) time, but you will only have a measuring standard when you finish the game. You can refuse to rest in dangerous areas, though this can make some parts a bit annoying.
In the end, though, the game would have been better (in my opinion, at least) if there were more consequences for resting in wrong places. Such as having things happen depending on how long you are taking. The random encounter we have can be a good consequence as well if you are playing ironman, or if you only allow saving after a successful rest. But after a certain level, I get the impression they hardly ever matter.
All this said, though, I still much prefer BG's reliance on longer term resources to PoE "per battle" thing. BG's system is broke, but it can be fixed by self restrictions in various ways. PoE on the other hand removes those longer term resources and no amount of self restriction can change it. Well, it could, actually, but they would resonate far worse than BG's...