We have three (formerly four, RIP) apple snails in our ten-gallon tank. They are highly amusing to watch. They will climb over each other to eat the algae off their shells. They often crawl right into the stream of bubbles from the airstone and use it as an express elevator to the surface. I have once even seen one of them climb the glass all the way out of the water.
They do eat some plants. Mostly they clean up the dead stuff. But fine plants like hairgrass or needle leaf ludwigia will get mowed down. They do also occasionally uproot plants without eating them. And floating plants, as mentioned in a previous post, will also disappear. I have seen the snails hanging on the glass and leaning back to reach floating plants. They don't bother the banana plant, the anubias, or the anacharis in our tank though. It seems broad leaves are safe. I think the anacharis is safe only because it grows faster than they can eat it.
But the most fun thing of all is "spoon feeding" them bloodworms. We use an eye dropper to feed bloodworms to our betta. And we discovered the snails love them too. They will climb the glass to get within reach of the eye dropper. If we drop extra bloodworms on the log or substrate the snails will go after them. Actually, bloodworms turn our tank into a free-for-all combat zone. The snails, betta, cories, and ghost shrimp all fight over the treats.