I believe in naps if you want to nap. Trying to stay awake when you’re sleepy just teaches you to ignore what your body needs, rather than putting you on a good sleep schedule.
This also applies (or should: the application is where I have trouble) to doing stuff you want to do: one should not repress impulses to work on interesting and/or useful projects because of some notion about doing something else first. Want to start the grading so you can say you started? Do it; never mind “write first.” Feel like writing? Do it; prep can happen later. Have a great idea for a class activity? Plan it; you can still get to the grading and writing, after the creative impulse is satisfied.
But . . . but . . . that sounds like selfish hedonism!
Oh yeah, baby. Oh yeah.