it wont be harmful just ugly when they slime all over the tank~ smash it when it's small you never know one day you want to buy an exterminator to kill the population, while harming your shrimps as wellz~~
"MTS and ramshorns are staples for many shrimpkeepers as they work on algae which shrimp have no appetite for. The strong dislike for them stems from owners overfeeding their tanks which encourage their populations to increase exponentially. snails are also great for helping the tank cycle as well as tell whether there is enough calcium available in the tank. Sort of like a canary in a mine shaft."
just showing a positive side to having snails in your tank lol. But if you don't like it just take it out or smoosh it. I have MTS in my tank just for the sake of having it mix the substrate around. You could also consider snails as a back-up cleaning crew for any food the shrimp miss.
If you want to have less problems with shrimp keeping then you ought to have some snails in the tank. When a snail moves around on the glass, rocks or driftwood, it leaves some slime behind. Microscopic bacteria starts to grow on that slime which is then consumed by baby shrimp. So yeah, snails are VERY beneficial to a tank.
I'm not sure why people freak out over snails beyond the original hype of them being unsightly. Reality, as others have mentioned, is that they're part of a healthy tank.
Pond Snails, Bladder Snails, Ramshorns, Nerites, et al all clean up waste and that's important.
The bit about leaving a slime trail while under water is probably more beneficial for snails than shrimp, honestly. Detritus and microorganisms for the most part are eaten by snails once they go back over the trail they left behind.