The factory exhaust system is so quiet that you can hear the parts moving around inside the engine.
At one time loud pipes added a small margin of safety, but now that car makers are insulating their passenger space to the point that you can't hear a fire engine siren right on your rear bumper, and the typical car radio has an output in the 500 - 3500 watt range, that isn't necessarily so anymore.
Anything that reduces the amount of engine power used for other things than making the bike go (such as pushing out the exhaust through restrictive pipes) will increase your fuel economy. That is a good reason to change the exhaust system.
The new bikes with the "900" (865cc) engine equipped with carburetors tend to not gain very much power from exhaust changes due to changes to the valve timing to reduce emissions. So, if a person were to change the pipes on this version for the purpose of increasing power, they are bound to be disappointed unless they also change the cams. The fuel injected 865 probably doesn't have this problem, but there isn't much information available on this yet.
You may like the sound of the factory pipes, many people do, so give it a try and then decide.
