Indispensable
Personally I have not (yet) had recourse to the use of the guarantee, but when you take a 500€ screen and you find yourself with a dead pixel in the middle of the screen, it's enough to make you angry.
I've never had this problem (my screen is still under warranty), but this warranty (although a bit expensive for my taste) is essential for me and allows me to stay calm in case of a defect not covered by the manufacturer's warranty. Remember, Asus takes care of 8 or more dead pixels, think about it.