My chin is not shaped for shaving. Even with the old Extreme3 that spot was tricky.
I just can't shave the very tip of my chin and the area right under it, wich in my case is kind of shaped like a w, so I have a slight "hole" under the chin.
Also the sideburns are tricky. How do you know exactly where to start shaving?
I still am noob so I only go with the grain at the moment.