I think it depends on which snails you have and whether or not you value your live plants. Pond snails will eat and damage plants and breed profusely. They feed on live plants as well as left over food so will multiply regardless of careful feeding. Malayan Trumpet Snails (MTS) don't eat living plants, only decaying leaves and of course left over fish food. Only if you over feed the tank will you get a snail explosion. MTS have the other benefit of burying themselves during the day which slowly turns over the substrate keeping it well oxygenated and less stagnant.
So, personally, if they are pond snails get them out and if MTS I would keep them.
Google them to get pictures, they are very different from each other.
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