If a player has been "on campus" for 18 months, he can sign a scholarship and NOT be counted against that year's 25. He will always be counted against the 85 maximum scholarships, but if he has been on campus for 18 months, he will never count against a particular class.
So, if you have a grey shirt that has means, doesn't seem ready to contribute, etc., you can ask him to go 12 more months and then give him a scholarship freed up by a player that flunks out, left the program, etc.