For the Wildcat, or the read option, or whatever you want to call it, it has to be used as a change of pace. It must be used to confuse the defense. Giving it a specific percentage, means you are scheduling it into the game, rather than using it based on a feel. If it is scheduled, teams are going to know that, and be ready for it, which will take away any chance it has to be successful.
The rhythm issue cannot be overlooked either. If the offense is moving the ball solidly with Mark Sanchez under center, switching to the Wildcat plays can serve to disrupt the rhythm that has been established, and can even stall a drive. You have to keep the ball moving while it is hot. If Shonn Greene just broke off fifteen yards, in between four straight Mark Sanchez completions, bringing in the Wildcat could be destructive. Mark clearly has a feel in this scenario, so even if the Wildcat play, or couple of plays is successful, the streak that Mark and his group are on can be halted when he comes out.
Rex Ryan has a better attitude about the use of the Wildcat. Mike Tannenbaum is doing a detriment by setting a percentage of plays. Despite being asked, he cannot give that type of answer. It is a bad idea.