Benefits of the badge are 300 badge points and the badge itself, which are important for the Badge Quest: www.sfimg.com/Support/Solution?catid=26444&id=222445
From the forum rules: www.sfimg.com/forum/tips
"WANT TO BE AN OFFICIAL FORUM GURU?
Get started by simply submitting quality posts with valuable content and/or that provide assistance to other members of the forum community. Such posts will be recognized by members of the Forum Guru Voting Panel.
As you accumulate votes from the panel, you'll enter the Forum Guru Leaderboard and you'll be assigned a leaderboard rank. Once you've reached the rank of 200 or better, you'll be officially recognized as a Forum Guru and your forum profile will sport the Forum Guru badge. IMPORTANT: You must have an account photo to be a Forum Guru.
Note: So that all affiliates have the opportunity to be recognized as Forum Gurus, points from the votes you receive will decrease 30% each month after one month. In other words, you can't just earn the title of Forum Guru and then stay there indefinitely without continuing to post and receive votes. To be recognized as a top Forum Guru, you must continue to be an active, posting member of the forum."