Loud cans are for attention whores ;D ;D

Though I have looked at a few for my er6, especially after the stock downpipe cracked at a weld.

Another advantage is often the reduction in weight. My stock exhaust weighs a ton, and when I took it to a motorcycle shop, they actually said, sorry we don't do car exhausts.. :

Aftermarket, slip ons, race cans, or whatever, cost quite a bit too, from what I've seen. The custom choice is always going to be expensive though; look at Pizza Hut for example.