FWIW, both 1 and 2 can still lead you in the wrong direction sometimes. For example, if you're working in a garbage-collected language most profilers (that I've used, anyway) won't give you good insight into how much time you're wasting on excessive GC load because you're creating too $#@$% many unnecessary objects (see: boxing), or creating objects with just about exactly the wrong life span. If you're working on parallel code, many profilers are darn near useless for figuring out how much time you're losing to blocking on synchronization.