If you follow it exactly you'll do a hell of a slow lap. Most of the corners are pretty standard racing lines but the braking points are waaaaaay early in half the cases and waaaay late in others and in most cases there's a faster way to do it. I use it as a rough guide to braking on long straights and that's about it - I know how far into the marked braking zone I need to be before I start braking (about half way down it in a GT06 at T1 Suzuka).
If you look at the speeds indicated at the corners, you'll get a good idea of just how slowly you're expected to drive