If you are talking about AT THE FAIR to show in market class, you want him light (withhold water and feed) for the competition. Many fairs "require" you to withhold for a certain number of hours there at the fair.
Of course, that helps in the show ring, but not so much if the animal is selling in a youth fair sale.
It's a balancing act. The better the animal places in the show, the higher $$ he generally gets.
You want the steer fed out to his maximum potential before you get to the fair.