User calls, says his PC stopped turning on. I arrive, ask him to demonstrate the problem.
Screen is black. He presses the power button on the PC and the one on the monitor. Wait a minute. Screen is still black. Try both buttons again, just for good measure, screen is still black.
Turns out the monitor was on but the PC was off.
Apple has largely solved this with their external displays, and the laptop industry has also solved this. Yet the PC world is still full of monitors with separate power switches that just confuse.
I like having my monitor off because of this one weird quirk that OSX seems to have. Specifically, the machine unfailingly wakes itself up from sleep every ~60 minutes to do something, and then puts itself back to sleep shortly thereafter.
When I'm trying to put _myself_ to sleep (and keep myself asleep), I don't want a bright-ass monitor briefly blazing across my room for no good goddamn reason.
Meanwhile, displays with indepdent power buttons have been around since decades ago and still tend to work that way with typical TV/media setups. Although that was always unergonomic and we now have semi-reliable HDMI fixes.
Apple menu -> Lock Screen, and the display will shut off after a few minutes of inactivity on the lock screen or by pressing the Escape key.
1) Turns off the display in 60 seconds or less. (I think it's more like 10 seconds or less, but I've stopped paying close attention to it, so I am no longer certain about the timing.)
2) Turns the display back on every single time I get a new notification, and turns it back off within a few seconds. Given that this machine is running the Work Messaging Client, that means that the display powers up and down very, very frequently.
So if this is the discoverable "turn off the display" feature that GP was talking about, it's not a fit replacement for the power button on the monitor.
(replying late for posterity)
At least you can use i2c directly over displayport. (how I change my monitor's brightness)