Who knows, maybe the final battle between Harry and LV will be fought in the prefects' bathroom! And Harry will defeat Voldemort because he'll open all the soap thingies and Voldemort will get soap in his eye and won't see what Harry's doing!
By the way, d'you think there's only one prefects' bathroom? Because in another topic, don't know which one, somebody calculated how many prefects there are at Hogwarts, and I believe it was at least 30 and probably more than 50. So yeah one bathroom is not much I think.
I wonder if the other ones are different from the one we know..
Maybe a sauna? Would be a fine reason to become a prefect!