This procedure should cut the power consumed "a lot" (whatever that means). Shutting off all video-related power consumers (with the sole exception of vertical deflection) is significant. The horizontal and HV circuits run hot, so turning them off can only be a good thing. Shutting off the CRT not only reduces dissipation further, but greatly increases its lifetime (no filament burnout, no screen burn).

As a crude estimate, I'd guess that the power consumed might drop by 40%.