Steroids get a bad rap in combative sports and from what I can tell, the use of steroids is greatly misunderstood. From what I have read, the greatest value of steroid use for MMA is in muscle recovery and for preventive health. More mat time and time in the gym, allowing you to cram a decades worth training into a 3-5 year time span.
Then again, that's also why you get 28 year old dudes with the blown knees of a veteran thai boxer.