yeah a redshirt is useful to save a year of eligibility for a player, if that player isn't needed for a season, for various reasons, including a lot of depth, inexperience, etc. however, if a player is redshirted for a year, and that player gets on the field EVEN ONCE during that year, his redshirt status is revoked and that entire year goes towards their eligibility. needless to say, redshirting a player is a tough decision to make sometimes