
If classes in the breed are small there is more satisfaction in placing in two classes and beating more dogs, especially if your shortly going into the higher class against those exhibits anyway.
We have small classes due to small numbers being bred in our breed and I feel more satisfaction being well placed in a higher class (even if I don't win the class) than winning a class of one or two in puppy or Junior.
Also if numbers are small going in more than one class can give your dog a chance to get it's act together in higher class, and therefore perhaps doing better in the challenge.
My first CC won at our club championship show (where it is very usual to enter several classes), with my Junior bitch I won 5 classes. She was a pratt in the first age class, a little better in the next, but then really got her act together for the higher classes she was in.
She went onto win the CC and RBIS, and of course there were fewer exhibits left unbeaten for the challenge. I doubt she would have done so well based on her performance in Junior.