From a couple other posts...

9.1.4. Off-Course Excursions
"The driver is required to follow the pavement or marked course during a competition, and shall not gain an advantage from an off-course excursion."

A few of the tracks I race at have "normal lines" that you could argue go outside the "marked course." I, like everyone else at the front, do follow the fast line which may or may not be the argued paved portion of the track outside the marked course.

What marks the course? A white Line, curbs, dragons teath, rumble strips, the edge of the pavement, the supplemental regulations, ...?

My examples:
Lime Rock - Uphill & West bend
NHIS - Turn 3 (Apex) & Turn 11
Watkins Glen - Turn 1
Road Atlanta - Turn 5 (? bottom of "S's")

Food for thought, feel free to add additional tracks/turns to the list of "off course" advantages that we all take lap after lap.

Raymond