I use the top-left corner in macOS for "Disable screensaver." When I'm pondering something on the screen for a while, I can just move the mouse there and not be interrupted.
When I use my Windows machine, it's probably the feature I miss most. I've asked my IT people at work, and they tell me there's no way to disable the screen saver on demand in Windows. I don't know if that's an OS thing, or just one of their policies.
Conversely, Option-top right corner activates the screen saver.
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Normally Windows apps can call SetThreadExecutionState to request the screensaver not come on. Video players do this, as do some other apps. See here[1] for a Powershell script that does just this, for example.
I suppose they could have deployed some group policy that disables this behavior. That'd be annoying if it's the case.
When I use my Windows machine, it's probably the feature I miss most. I've asked my IT people at work, and they tell me there's no way to disable the screen saver on demand in Windows. I don't know if that's an OS thing, or just one of their policies.
Conversely, Option-top right corner activates the screen saver.