-they look after the hens
-they are very beautiful (nature generally makes males more attractive, buggers!)
-they fertilize the eggs (only a pro if you want to hatch eggs i suppose)
-noisy (crowing) so dependant on your location to your coop/neighbors might be an issue
-as chickenmaven said to much attention paid since so few hens, i have one boy who was only with one hen and he picked the top part of her head bald (hanging on). i have a few trios that are great (no hens missing feathers or anything). so depends on the birds i guess.
Don't count on a chicken from the feedstore as being a show bird. Even if they call it so. You need to look at photos of better quality birds and read the standard to have a fair idea of what you are looking for.
In general, you want a nice crest, 5 toes per foot, black or slate skin, mulberry to black walnut comb, as much foot feathering as possible, silkie feathering throughout. Wings should be held close to the body, and fairly horizontal. As few hard feathers in the tails, wings and feet as possible. A broad breast, shorter back. Not too long a neck.
If you are not planning to show him, and he will be free-ranging with his hens and protecting them as a good rooster does, he needs good vision, which often means a smaller crest, or trimmed around his eyes.