I've only taken advantage of a courtesy a couple of times, that was when I had my Civic Hybrid, and the Honda dealer was 30 miles away.
They did point out that there was a £500 excess on the insurance in the event of an accident. After the first couple of years I got it serviced locally.
Beiing retired having another car, and within a three minute walk from my Lexus service centre, thankfully I am no longer in need of a courtesy car.
Also as I've found with my other car, not being in need of a courtesy car, gives you more flexibility of when they can take your car in.