Snails good? or Snails bad?

I love snails.

Malaysian Trumpet Snails are the most "plant friendly" of the smaller
snails.
They clean thr detritus off the bottom, and consume their weight in algae
daily.

Rams horn snails are plant killers.

I fix that problem with weather loaches which will "hoover" the rams horns
out of the shell, but don't seek to kill all the MTS.

My fav. plant for a background is Java Moss.
It also reduces the ammonia / nitrogen load of the tank and gives fish a
high fibre diet.

It grows faster than my fish will eat it. A good addition to any tank.

I am very certain that the answer depends on the type of snail in your
tank. My experience with snails in my tank has been good. They are
eating the brown slime on my plants and gravel. Incidentally, I have
no idea where they came from. The don't seem to be related to the
Apple Snails that I bought, which all died.