For knowing the driving line on a track that I've never been on before, then that is a definite for me as I can 'draw' out a line in my head as I go along. The one thing I don't like about most course creator tracks is the sudden elevations with poor visibility, making me overshoot corners that are directly on a hill because the car lifts up off the ground leaving me with no control over the car.
If the course creator tracks had better visibility, more visual reference points on-track and less sudden elevation changes that lift the car off the ground then I wouldn't mind custom made tracks. For now, I avoid them whenever possible.