So you can access things outside, helps in docking, getting up to the bow, throwing bottles at seagulls, whistling at bikini babes, all kinds of things
Probably if you're clever you can just swing around in the chair and take a leak over the rail. All kinds of things. I wouldn't suggest attempting that while underway or in a crowded marina but to each their own.
Yes, if there was water that was around due to heavy conditions, rain and other storms or some schmuck wizzing out their door as you pass by there would be some moisture, but generally it's closed up and there are tracks, guides and enclosures to ensure the operator doesn't get much (if any) water through there.