It's healthy for you. It really is. Nothing wrong with doing it as long as you don't do it like 3 times a day or when your right hand (or left, which ever you use) gets twice as big as your other one.
Yeah I do it abit too much probably, but then again I don't know how much is too much.
Morning: 2 or 3 times
First break in school: one time in the toilets
Second break in school: once or twice in the toilets yet again
Home: when I get home
Night: 2 or 3 times before I sleep.
And the occasional wake up in the middle of the night and let one off.