I don't understand why people play with their VSync turned off, or would want to turn it off.
If you have a 144Hz monitor and a good enough CPU to run Renegade at 300 frames per second, the game will render 156 extra frames every second that you'll never see. Because your monitor is designed to display only 144 frames a second, it wastes power & makes the fans spin hard to produce 156 frames that you won't see anyway.
VSync caps your FPS to your monitor's refresh rate, so your computer won't work extra time to do stuff you'll never see.

Game logic is literally: "If VSync is enabled, cap FPS to monitor refresh rate, otherwise cap FPS to 300."
Disabling VSync doesn't yield any noticeable difference, except for making your room warmer.