So far, in my big tank, snails are the only thing that'll eat through the hair algae growing on the back wall. Now, granted, they're not very efficient at it, and it would be much quicker for me to just wipe the junk off, BUT me being the strange person that I am, I rather like looking at the little trails they create when eating.
I guess all that means is that it is definately a matter of preference.
Lately, though, my Leopard Cactus Pleco seems to be eating the snails. I only guess this because there seems to be a large quantity of dead snail shells right next to and inside of his cave.
I like the snails because there are the occassional fish who like to eat them, and mine have yet to actually bother my plants. But then, there are plenty of snails out there that will gladly munch on your plants. -If you intend to keep the snails you have, you should do some research and see if there is a high liklihood of them eating your plants, and make a decision from there.