Go ahead and ask a specific question. There are all kinds of expert opinions here.
If you are referring to rules, most venues have a rule that says the exhaust must be directed away from the surface.
However if you are referring to aero, there was a thread that I can remember where there was a discussion that the exhaust be directed around the laminar flow of the bodywork to reduce drag.
And of course exhaust could be used to fill the aero hole in the back of the bike.
Don