My pipes are wrapped (pics coming once the paint is done).
On a motorcycle, it's usually more for "hot rod looks" than anything.
It doesn't have to be wet...we usually wrap pipes dry, but you can optionally wet it to help make less of a mess. On a bike, the heat and the open exposure will take care of an excess moisture pretty quick (you will, after all, get them wet in the rain at some point).
I chose to wrap mine partially because I personally love the look and partially because I modified my stock headers to make custom pipes and wrapping them was MUCH less expensive than chroming or ceramic coating given the extent that I modified the pipes.
2002 ACE 750 Deluxe
The Skunkworx Custom Cycle