When you rescue from a shelter you are saving a dogs life. This is clearly the biggest benefit of choosing this option, however, there can be some drawbacks to adopting at a shelter.
Pros
1. You will be saving a life. If the shelter is a kill shelter then you will be keeping the dog from being put down after the maximum allowed stay. If they are a no kill shelter you are saving them from living in a cage and giving them love and a forever home.