I only use it to learn new tracks.
In my opinion, driving line AND flashing gear indicator should be banned van GT. Now everybody (including less talented racers) can predict the breaking point for every turn by just looking at that stupid red flashing gear.
Of course it will never be banned from GT, I know that.. But in GT4 you could turn in off, so why nog in GT5P?
At least ban it from online expert races then. LEARN your tracks instead of being guided around them!