Supplemental Information

Usually, in addition to 2-3 required essays which we must finish for our applcation, a school also gives us an opportunity to write an optional essay in which we can put some "Supplemental Information" about our academic background as well as career records.

My question is: how many words should we put in such an optional essay? If the word limit for a required essay is say 500 words, should we also strictly stick to the same wordlimit in the optional essay?

I shall apprecaite it if you can give me any advice.