We have a doggy door and we love it.
We have an attached garage and the back door leads right into out dog run. Our dogs think that they need to go out side evey two hours. Before we got the doggy door we would just leave the door open, but it was exhausting and frustraiting dealing with the birds coming in and building nest and crapping Everywhere. It was nasty. So, we had to do something. Before we installed the doggy door I built a gate in the garage like a bifold door to separate their access to the garage but gives us access when needed. It prevents them from doing their business all over our garage floor on those bad weather days.
We plan on putting another on in the door that attaches to the house so that during the summer they have full access to the dog run. My pups are tea pots so there is no threat of birds of pray. They bark like lunatics when they see a racoon, opossum or rabbits so we dont have to worry about that either. We've lived in our home now for 17 yrs and have only had one incident with a racoon who would come to eat our grapes. Grape vine has been gone now for eight years so, no problem their now either.
But for those of you who have wee little pups I would definitely think twice about giving your pups access to a dog run or yard through a doggy door unsupervised. Fortunately we dont have to worry about that.