Well, apparently it makes fishing more successful, (but Minecraft fishing is even duller than real fishing, so nobody actually does it, and certainly not with auto-heal enabled).
It makes farmland wet, but ... so does a dumping a bucket of water in a hole, and that lasts longer (i.e. indefinitely).
I'd never gone underwater, though thinking about it, now essentials is installed I haven't been able to get out of Lava and survive like I did in the past.
