Saddle set back is critical in positioning your body mass fore and aft, and as noted above, most people have it set too far forward. If the saddle is too far forward, you will have to support your body with your arms, which is not good. You should have as little weight on your arms as possible. Too far forward and you will also be falling forward onto the nose of your saddle.

Adjust fore and aft by feel, not by using strings and plumb bobs. Move the saddle back until, when you are in your normal riding position on the tops of your bars (not hoods or drops), you can just lift your hands off the bars and ride no handed without falling forward.