The degree rotation number shows how many  full circles you can get from your steering wheel. For instance 900 degree means you can get 2 ½ turning times lock to lock. Which is more than enough for any game and driver.
To be honest nobody needs so much spin, but believe me better more than not enough. And I am talking from experience. I went through 3 steering wheels with 180 degree rotation before I realised that the only reason for not been able to turn on time and all that under steer was  my wheel rotating length.

Not to mention that you end up braking them eventually. This is what has been happening to my  old ones. And I still can not believe it really took me 3 wheels and around £200 to realise that. Seriously not having enough rotation takes you nowhere but back to the game shop again. Wheels just brake when you get too exited behind the them.

No more of these problems when you get a 900 degree rotating wheel. You wont have to worry about not having enough steer or trying to be too careful on the wheel worrying it will brake again. You are more relaxed and presumably more focused on your driving.