Creatine is used to boost your high-intensity performance. It's been proven by guys in white lab coats that creatine will increase your performance in repetitive cycling sprints. It's not going to improve your endurance, but it will help you with speed in short bursts. And, unless you pump out hundreds of reps with pink dumbbells, you're going to see gains in your lifts. You lift in short bursts: You do a set, rest, do another set, rest and so on.
Let's step outside of the gym for a moment: creatine can benefit you in ways that aren't fitness oriented. It may be beneficial to use creatine for muscular, neurological and neuromuscular diseases, like arthritis and congestive heart failure. Creatine helps to reduce "muscle wasting" in post-surgical patients. If you're lying in bed, not using your muscle, you're bound to lose it. It also will reduce heart spasms and may lower blood lipids (cholesterol).
Dr. Caroline Rae led a study on the effects of creatine on your brain functions and found that it can improve your memory. She had her test subjects supplement with 5 grams of creatine a day, for six weeks. When tested, the subjects had an increased ability to remember long numbers and their brains operated a lot faster.
Studies have shown short term use of creatine supplements to be safe and it's not banned by most sports. So to sum it all up, creatine is safe, you're allowed to use it and it can be very beneficial.