I was surprised by the massive help that having an "in" to a school had. My PI knows my supervisor from undergrad well, and another prof of mine very well, and their recommendations about me were crazy useful. The PI was talking to me like I was already working for him before I had even finished writing my application, and literally the day my final supporting document got into the school they sent me my acceptance letter.
It all happened so quickly that I didn't even apply for any other schools. I made it into my top choice and had funding, under a fantastic supervisor, why would I bother putting myself through more grad apps?