It's really up to you whether you want them or not. On the plus side, some species do a fair job at cleaning algae; they feed fish such as puffers and clown loaches; still other fish will eat the eggs; they are a natural part of the ecosystem; and some folks just like snails.
On the down side, they add to your bio load in the aquarium; they can reproduce to the point your tank becomes overwhelmed with them; some do very little to clean algae.
So, it's up to you whether you like them or not. There are many different varieties, so maybe there is one that you like over the others. Try it and see if it cleans the algae enough for you. If not, squish it against the glass, and let the fish eat up, most fish will really go for squishy snail guts, it's a nice meaty treat for them.