Is full exhaust better than slip on?

A well-designed and tested full exhaust system can provide increased performance, power and speed. A set of slip-on mufflers is much less expensive than a full exhaust, and offers a change in sound and exhaust flow, as well as appearance, but not necessarily much change in performance. A full exhaust system requires much more skill (or cost if you are paying a shop to do the install) and effort to install, whereas a set of slip on mufflers can be installed easily using common hand tools.

Do I have to tune a motorcycle for an aftermarket exhaust?

Adjusting your tuning when changing out your exhaust system is good practice, as it ensures a fast and responsive motorcycle. With modern, fuel-injected motorcycles, ECU tuners for Harleys make tuning your motorcycle a breeze. They plug in to your stock wiring harness and connect to a smartphone for on-the-go tuning for maximum horsepower and top speed! For carbureted bikes, changing the carburetor jets to add or remove fuel from the throttle range allows precise tuning for optimium performance.

Do I need a muffler / resonator on my exhaust?

Removing your muffler (aka resonator) will change the tuning of your motorcycle, as the back pressure ties into the performance of the engine. Typically, vehicles will run just fine without a muffler, though you may be in violation of local noise ordinances, as it makes your motorcycle MUCH louder. Running straight exhaust pipes (no muffler) on motorcycles is pretty common practice. A universal baffle can be easily installed in a straight pipe to help reduce the sound, though it will not be as quiet as with a muffler.