I respectfully disagree.
Generally speaking, if you want a happy, healthy, "professional" quality dog, stick with one. A working dog is happiest when they are partnered with a human that actually with them daily. Any temporary rest they need is the responsibility of the human partner to provide (in the field) and doesn't require days of rest if it's regular work. Training is best if repetitive, regular, always the same and always the same human partner.
I was partnered with my Service Dog for 12.5 years. No two dogs could have provided me with such perfect service on a daily basis. Police protection dogs are partnered with one human partner to maintain training levels. Same for Bomb dogs and Drug dogs. There is no reason to have less in our work.
By the way, a partnered dog will often suffer separation anxiety if/when the human partner leaves them behind. They can't understand what they did wrong and why they are being punished by being left behind. That is one of the reasons why a Service Dog is allowed to sleep in the hospital room when their human partner is there. Sometimes it needs to be about what is best for them, which always ends up being the best for us. :2cents: