Consider each request on their merits before taking action. I've knocked back requests from people that I know absolutely nothing about. On the other hand I've accepted requests from people I don't know but where we have mutual friends, and later have met them face to face and made new "real" friends that way. If you're doubtful before accepting have a look through the applicant's posts on your friend's threads and see what impression you form.

Then sometimes you do have to hide somebody. A person I met in real life through a mutual friend was good company then later became a FB friend. All she ever posts is dozens of You Tube links which are of no interest to me and clog up the page.

Also there are real life friends who have fb accounts but don't seem to be active. We meet face to face but have never enfriendified each other online. If they're not using it there seems to be no reason to.