Sometimes it is better to stay in gear past peak horsepower as shifting wastes time.
In other intances it is better to stay in too high of a gear, not downshift, and fall out of the power band.
For example my lap times only improved ~.5 a sec when I would downshift, rev it out and upshift. Considering engine conservation, gas conservation (for endurance racing), and the possiblity of missing a shift it is sometimes better to stay in the higher gear and be a little down on power.