The more modifications your bike has, exhaust, filter, cams or other engine mods that change the shape of the fuel curve, the more improvement you will get from dyno tuning your bike. With carbureted bikes this is mechanically done by changing the jets and needles etc. On EFI bikes this is achieved by electronically re-writing the fuel curve in the bikes ECM or via after market control modules that 'piggy back' of the bikes ECM. With EFI you have more control over the fuel curve than with carburetion, i.e. you can improve deceleration popping without affecting idle. You cannot do this with carburetion.
On a completely stock bike the fuel curve is usually fine at 100% throttle, however at lower throttle openings the fuel curve is usually lean. A full custom map on a bike like this would make no improvement at 100% throttle, therefore no peak horsepower gain. However in the lower throttle openings where the fuel curve was lean, the bike will run smoother, cooler, and have better throttle response providing a more confident ride. If you did before and after part throttle roll-ons i.e. you might see a 30% increase in power.