
I think it's breed dependent and with breeds with small entries like mine entering more classes for the competition is more usual at club shows, though the second entries at general champ shows are becoming prohibitively expensive, often at £5.
Can't see how they can justify that for a repeat entry in a breed class, the cards have already been printed and the judge has already gone over the dog in it's first class, so just has to fit it in order of merit as a seen dog, no extra cost to the society.
The day I won my first CC with my first champion she was entered at our breed club champ show in Junior, Special Yearling, Graduate, Post Graduate and special Beginners. It did mean she knocked a lot of bitches out of the challenge.
As a friend just starting out had entered and won Puppy, Novice, débutante, and was only beaten by mine in Junior, there were very few bitches in the challenge, which may have been an advantage.
If your youngster is like most of mine needing to settle, it can be advantageous to enter more classes so they finally settle, on the other hand an easily bored exhibit may be best in one class.