Some people hat snails in their tank, personally I don't mind them. They eat algae and dead leaf matter. There is a myth that they eat plant leaves(helthy ones) I don't buy it.
Malaysian Trumpet Snails are beneficial to a planted tank, cuz they act liek worms do in a garden, by mixing around the soil, and eating nasty stuffs under the substrate.
Pond snails are the ones peeps say eat healthy plants.
Ramshorn snails eat algae.
The MTS snails you'll see once in a while. The other two you will see all the time and there nasty little eggs all over. You could always get some predatory snails..jeesh forgot the name of them, but they will reproduce also..haha
Snails will come with your plants btw, so be prepared, unless you get some snail killing dip before introducing the plants to your tank.