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The reset button must be the safe winner in any contest measuring a uses/usefulness ratio since it's omnipresent and fully useless.
Not only on the contact form. I can't also find the benefit of reset button in any type of HTML form, IMHO. But I tend to put it every time I create a form :)
What if I says it IS useful? But not in every form.
I use it with the "UPDATE" part in a CRUD application sometimes.
Say SO for example, I hit an edit link on a question.... and made some edits and reread it... but then I decided it is not a good edit... I have to reload the page or go back to the last page and hit the edit link again to get the original text.
Whereas, if there is a reset button slapped there, it'd be easy.
And there is always CTRL+Z.. so why not?
There are some good uses but just don't slap it in silly like what most ancient HTML books would teach you to.