Again as Fresh2o stated I dont know anything that consistently eats waste.
My tank is 99 percent algae free. Algae free.....to my eyes. Meaning algae spores and hyphae is present that I cant see. Snails imo
are more of a preventive action than curative. People get algae then wanna know what snail or fish to dump in. Snails as many mention eat dead/dying plant material....dead/dying material creates ammonia ....ammonia creates algae. Snails are opportunistic. Much of their diet we can barely see or not at all. Biofilm makes up part of thier diet as well.
Too my eyes I see nothing in my tank for them to eat. Yet they prosper without me purposely feeding them.....id say my tank has 50-60 percent plant mass. Most tanks are probably in the 25 percent range. So if you have large plant mass with large snail population there is a balance. Wouldn't it be this way in nature?
But if I have say the same 300 snails in a 10g with two pieces of wisteria....not natural. Perhaps not enough natural food source. Not enough in tank to support them. This tank got like this by the aquarists wrong doings. Could there be plant damage in this tank.....yes.
Autumnsky brought up a good point...majority of plants said to be damaged by snails are really fish...some just curious.