on windows i'm running a triple monitor setup - center for the IDE, left for logs, debugging and documentation and right for communication (email, chat).
sometimes, when i play games i wish to turn off the peripheral monitors for better immersion; also my graphics card is probably happy having to render a few million pixels less.
usually, i just used the physical buttons to turn the monitors off, but after a defect i've had to get a new one that places its on/off switch at the back, which i can't easily reach.
nirsoft to the rescue: enable/disable or power on/off monitors over software with MultiMonitorTool