I added plants one time that had a snail on them. I only saw one snail and decided to leave it in, not knowing how fast they can multiply. About two weeks later I had dozens of snails and thought it was going to cause a problem. I started pulling them out a few at a time, and when I saw a clutch of eggs I would try to remove that, too. However, since I added apistos to the tank I think they eat the snail eggs. I know nobody would probably believe this, but I think my otos eat the eggs too. I haven't seen any eggs for over a month and the snail population seems to be in check.
Snails are like roaches. They really don't do any harm but they multiply like crazy and once you have them you can't get rid of them.
Snails do add to the bioload though, so even though they may eat algae or leftovers, they poop a lot, too.