
Everyone will have different views, dependent on what breed thay have. And Barbara is so right about the gap between seasons - we get no guarantees.
I have a breed that is mated on their second season. But I like all my bitches spayed by the time they are 4. Huge difference to the large breed owners.
My best bitch had a litter in January one year, and had her next season in rather less than I would have expected. By the time her next season came around and I wanted her mated to a specific line, I bit the bullet. And have no regrets that she had her next litter less than a year after her first. Her next litter was born in December, a few weeks short of a year.
It wasn't a back to back mating, but she was in top condition, and had only reared two pups, so mating her again for another 2 was my best shot. I won't breed from my bitches after 4, there are far less whelping problems if they are bred young. And having 2 litters before spaying is not overbreeding them.