Showing in what? Open, Junior handler, APA, 4-H?
The junior showmanship and 4-H classes, the birds must be well trained. Open APA, not so much (unless they are Runners), but you want your bird comfortable enough in a small cage that it doesn't freak out by being confined.
If you have chickens, they must be comfortable enough with being handled to allow you to bathe them.
Birds who are alert and calm show better. It's not so much that they get preference, but they are easier to see and evaluate. If the judge can get a really good look, they have a better chance of winning than a bird that the judge can't get a good look at.