longer version: our bikes come with some kind of map on the ecu from the factory. that map will have lean spots and rich spots at a variety of throttle settings. It's close, but it's a lot more about emissions than proper mix (which will give you both power and longevity). By getting a power commander and getting it mapped on a dyno, you get the bike set up so that it runs optimally with your mods (or even stock, it will be a better torque curve everywhere).
now notice I wrote dyno tuned. That's important. if you get a power commander and throw a downloaded map for similar mods on, you're basically rolling the dice on fueling. You may fix a flat spot and make another one. You may start running pig rich, etc.
The autotunes on the fancier models, are good enough for street. They may eventually get you to a close ballpark of where you should be. However, because they're glacial to adjust, and can get... disoriented... by temperature events or changes in pressure, you will likely end up back at a stockish map with some adjustments.
would I spend the money on a pc3 or pc5? absolutely. Would I spend the money for someone like triple strong or speedwerks to set it up on the dyno? definitely. Would that be the first thing I did? No, I'd start with suspension and brakes. And probably wait till i'm further from stock (full system, cams, k&n, whatever)