Not exactly, they add to the overall bio load and produce waste, however they do clean up the tank and eat a lot of slime and crud. Just makes sure that doesn't clog ur filter up.
I have small snails in my sump also. They have been there a couple of years. I don't know what kind they are, but they have never migrated out of the sump or maybe they have and gotten eaten by the cichlids.... I have never had a problem with them...
Both of my canisters are filled with snails. However, there are none in my tank. I clean each filter once a month. I remove as many as I can. I used to remove them and feed them to my puffers in my saltwater tank. Theyve been in my canisters for many many years...no harm caused just remove 'em when cleaning.
Snails are cool. As long as they dont start to populate the tank, let'em be. They eat what others drop....
I have had them in my sump for a long time. They cling to the filter socks. I shke them into the main tank and the fish get every single one.