My sister has an automatic feeder for her cat. It is designed to drop only a certain amount on a timer. I don't know if they all work this way, but as long as the feeding is regulated it shouldn't lead to weight problems.
I see these as more of a solution if you are gone all day--like for a wedding or something. You know you won't be home at the right time. It could also be useful if you are away and have someone looking in on your dog each day. Beyond that, I don't see it as a solution for every day feeding.
I don't use one for my dog. She eats when I feed her. I refill her water as needed. I don't really need one.
