i would leave them loose- especially with calves possessing structure that is questionable to begin with. Even if the only exercise they get: is turning in a 16x16 circle, it is more than shifting from left to right.
When you have a show string of livestock, who are on the road nearly all summer- not only do they tire out towards the end-- but any hidden, or slight structure problems really show about state fair time-- the worst to have that appear.
When we were showing real hard-- we always stole gates at the grounds to set up pens to leave the calves in overnight outside, and we opened up alley ways to run the lambs back and forth.