Creatine helps runners in 800 meters or shorter events by boosting power and short-burst energy. Longer-distance runners get the same physiological benefits, but other supplements may help more with endurance. It's safe at low doses.
If you are a runner and you're trying to figure out if creatine is yay or nay for you, here's my two cents on that. If you are running an 800-meter or below, creatine is fantastic for you. Creatine helps with increased power output, helps you in the weight room, helps you have short bursts of energy. You need that. Even if the 800 is not technically a sprint, you're still freaking running fast. Now, if you're an endurance runner, 1600 meters or above, creatine can still be awesome for all of the benefits I just went over. However, there are supplements that are maybe even better for your performance than creatine would be for you. That being said, creatine's not gonna hurt you. It can only really help you. So if you're interested in it, just take a low dosage and it won't hurt you at all.
