I agree with ZPitcher that joint cracking can be beneficial in keeping healthy joints especially as I am not a very active person as I do most of my work sitting down at a desk. Alot of people who sit at a computer for hours at a time have pain in their wrists, back or whatever. I have no aches or pain to complain about, however, and when I do get active there are no adverse effects (except maybe sore muscles lol). I credit that to a little stretching and joint cracking.
Alot of my joints crack, not just my elbows. I believe its because of the stiffening of my joints when I am not very active, like when I am sitting at my computer. When I get up after half an hour or so and stretch a bit all my joints crack or pop. They range from huge cracks in my knees and shoulders and tiny crackling in my spine and neck area. It feels sooo good!
Cracking also happens when I overuse a joint, like say when I spend two hours furiously writing with a pen or pencil. The finger joints stiffen, especially my forefinger and to get it mobile I have to crack it. This is when it hurts to crack. I'm not a knuckle cracker though, I try to avoid it whenever possible, so maybe that's why I get pain in my fingers then. I find that cracking my wrist makes my hand feel better, so I do that every once in a while as a preventative measure.
Cracking my shoulders also makes them feel them and the upper back area feel better. I think that there is a minor area of effect that relieves pain or stiffness around the area of the joint you are cracking. Combined with stretching, cracking joints is an effective way of relieving stress on your body. I do caution, however, that you shouldn't force your joints to crack, and that they should crack naturally when you stretch. Forcing a joint to crack can be very painful, and I say this from experience, and painful means harmful. A good way to crack a joint is by stretching, say your arm, and then rotating and while moving it, your arm, to the side or whatever.