CRTs were in use for decades.
In the early 1990s, there was no power saving. You could turn off the monitor with the front power switch, or use the screensaver.
A few years later, power saving options began to be introduced. The computer could signal to the monitor that it should go into a low(er) power state. Turning on again took at least 5 seconds for a visible picture, sometimes 15-20. That might not be appropriate if the computer had to be used in response to something like a phone call, or visitor at reception.
