My goldfish LOVE snails. They like them so much that I now breed snails in my 120ltr and net them out once a month for the goldfish to eat.I'm afraid my goldfish might kill them in the freshwater tank...so I haven't tried in that tank.
I also like the look of the snails in my tank, I think it gives the tank a really natural feel (well, as far as glass boxes go) and they eat the decaying plant matter which means I don't have to shove my hand in the tank as often.