I like HeroLab not because it keeps me from having to know the rules - in fact, I've picked up a lot from using it through checking things HL throws out that don't seem to make sense to me - but because it instantly lets me see all of the effects on my character when I change stats, add a feat or a piece of equipment, etc. I have a strong tendency to make sub-optimal choices in favor of fluff, and HL lets me see just how sub-optimal so I can keep it from veering into 'suicidal.'
Cost can be prohibitive if you want everything at once now that there are so many add-on packs for Pathfinder. I can't remember how much the demo (free) version allows you to access, but the key difference is that with it you can't save or print characters.