When I got into the planted tank hobby, I considered these creatures to be evil. Every little snail that was in my tank either got sprayed with hydrogen peroxide or was removed and thrown in the garbage. What an idiot I was for doing such a crazy thing. At this point, there are three tanks in my room and everyone has snails happily enjoying the aquariums. I cannot stress the importance and benefit of these little guys when it comes to consuming dead or dying leaves. Instead of me trying to get between plants with a net, the snails will do it for me by devouring the decomposing matter. Don't get me wrong, these things can multiply out of hand so you will need to periodically destroy some of them but don't even bother with trying to eradicate the snails. My shrimp get some crushed snails from time to time and they really love snacking on the delicacies.
So yeah, some snails like Ramshorn, Pond, MTS are definitely not harmful to a planted tank but are rather beneficial. Did I mention that they eat algae too?