Pros: Rescue dogs, in my experience, are so thankful to have a good home and are extremely eager to please.
Cons: You never know fully what you are getting into. For example, one of our rescues was terrified of forks
We knew he came from an abusive environment, so finding out all these new things that he was afraid of as time went on, was very heartbreaking. It just makes you wonder exactly what they've been through. This same rescue also had an extremely short life - health is never a guarantee, but it does help if lineage is known and parents are health tested before breeding (which you will get with an ethical breeder).
Cons: You never know fully what you are getting into. For example, one of our rescues was terrified of forks