The advantage of using Creatine is the ability to lower the sensitivity of fatigue in the muscle. Drinking it before a workout gives you a boost of strength and helps retain water in the muscle to allow protein to travel into the muscle as you lift. It also allows you to lift heavier without feeling as much pain. Consuming after a workout helps recover the muscles quicker as well.
A disadvantage of using creatine is of course, the retention of water in the muscles. Your muscles will look bigger yes, but it will also be swollen with a bit of water, so definition can't be seen as much. If you're a competitive bodybuilder, it's safe to drink creatine until the last 3 days of contest because you want to lose all that water quickly.
Remember that creatine is not a steroid, like some people believe. It may sound like it is, but it isn't because creatine is found in beef and isn't created by the body. The average person consumes 3-5g of creatine, an athlete consumes 5-10g and a bodybuilder consumes 20g usually. Also, it'll only work if you have a proper diet and workout routine. Otherwise, you won't really see the results.
Negative: nonmuscular weight gain, cramping, strains and pulls due to overwork, dizziness, stomach pain, loose stools, high blood pressure, liver problems and compromised kidneys.
Positive: you will gain weight, and you will gain it quickly. Creatine pulls water into the muscle cells in order to increase protein synthesis.