Also, something worth mentioning for nVidia users:
I've been using it for quite long time without any adverse effects.Option "OnDemandVBlankInterrupts" "boolean"
Normally, VBlank interrupts are generated on every vertical refresh of every display device connected to the GPU(s) installed in a given system.
This experimental option enables on-demand VBlank control, allowing the driver to enable VBlank interrupt generation only when it is required.
This can help conserve power.
Default: off (on-demand VBlank control is disabled).