Twice I had delivery scheduled for a specific 4-hour window on a specific day, and twice that window was disregarded. The first time the delivery came 3 hours late (I had left home by that time); the second time delivery arrived 1 1/2 hours after the window had ended. The delivery itself went fine, but missing those windows twice in a row is inexcusable.
Pros: Actual delivery went fine
Cons: Missed two delivery windows - inexcusable