AES/newspost wrote
Anyway, I'm assuming that "Jackpot 1243" wanted to move up and down
freely between 39,000 and 41,000 feet seeking smoothest ride and best
fuel economy without having to make repeated requests; and Denver Center
was willing to approve this since nobody else was up that high anyway.

Is that likely the case?

Well, sort of but not quite. I think what he really requested was a
block altitude, which is the standard phraseology, and the goal was
not to intentionally change altitude but simply to avoid having to
correct the altitude all the time when turbulence changed it for him.

When a pilot requests a narrow block, it's usually because the ride is
unavoidably rough and he wants to be able to just hold a pitch
attitude rather than continually changing pitch and airspeed to
maintain altitude. It's easier on the airframe, easier on the
passengers, allows you to maintain a relatively constant airspeed so
it might be slightly more fuel efficient, and generally easier on the
pilot as well if he is hand-flying. I routinely ask for this when I
fly in convective weather, and so far I've always gotten it. Like
this pilot, I also generally ask for a 2000 ft block.

Michael