Turning off V-sync murders GPU

[Winnz]

As the title suggests, if you turn off V-sync in the settings, the GPU will crank up to full 100% usage, even if the graphics are at low.

 

[4RM3D]

Turning off v-sync also removes the frame rate limit, which may be the cause of the decreased performance. Regardless, there is generally no downside to enabling v-sync, so why turn it off?