You really don't need to smoke any more weed until a couple of hours after the last time you smoked (if you are smoking joints that is, mostly by yourself but no more than 1 other person). If you're using a bong then you know to hit it again once you just feel really tired and worn out. Well that's for any method of smoking weed but with a bong that feeling comes sooner than with a joint (because you moked less weed). I could be wrong though, it's just that I'm used to smoking king size joints by myself all the time.