Why would someone run dry exhaust versus wet? Probabaly a stupid question, but i didnt even know that some boats had dry exhaust. Fairly new to the game.

Keeps the water out of the tailpipe. Gives you some more power because there is nothing blocking the exhaust. Also you can run a bigger cam since reversion is not a problem as long as pipes are over transom design. Downside is they are very loud.
Also they do still have water in the header. So not all dry just does not dump water into the tailpipe.

And the other downside, dry header exhausts are pricey.