Since it seems we're primary talking about the t1 and early t2 stage, I don't think it makes a huge difference on most maps (primary talking about 15x15+ maps since on 10x10 you either walk most of the times in teamgames or in 1v1s you can't see every drop due to lack of attention). Like, you don't have a t2 radar that early, therefore can't rlly see drops until they're close to the land anyway. You don't let your intis just patrol around over non-Aeon frigs for no reason and therefore it doesn't make a difference if the transport pops up 10m away of the land due to radar range or if it popos up 9m away of the land due to underwater-transports.
I simply fail to see where the benefit is. The only thing is that random scouts can see a transport but that doesn't happen that frequently if you watch out / use your inties like you should.
Also on many maps the water is shallow, making it a pain for the transport (pathfinding issues, bugs, ...) anyway.
Other things are how units react. E.g. can you getto a sub? And stuff like that, but those mechanical/balance stuff isn't my problem.