Selecting low gears at high speeds bad for the car?

[Monk]

I always down or up shift (even "skipping" a gear in sequence). I need to make a video to prove it/showing what I mean but staying in 4th from 50 to 20 before going to neutral or 1st/2nd helps stopping power and gas mpg. Hitting neutral at 50 and coasting has ill effects not seen till time has been given plus worst mpg.

To add to @Darkout (s) post, "Ill Effects", if we don't down shift one gear at a time, we're running the gamble that if needed to get the best response gear "For both" engine braking & accelerating, we need to be in the correct gear, or "KNOW" by glancing at the speedo what gear to select at the time so it not only goes in gear smoothly, but to be at the right rpm to accelerate.
Things can change while we're coasting, we need to be in the correct gear.