I agree that by being in circles you see many more items than you would ever stumble on without them. In addition, if you create treasuries, many people in your circle will see it that might not have seen it in the past. Of course, you reach those people who happen to be on their feed when you post it. As with email, posts slip out of sight pretty quickly, so if someone has alot of circles, more people will be posting at a given time and anything you post, will move quickly. Still, you're reaching alot of people you might not have reached before, and every little bit helps exposure:)