For multiplayer games I leave it off. I honestly can't remember seeing tearing in RO2.
The few instances where I do switch it on is if I'm playing a game with smooth sweeping camera moves, like cut-scenes or racing games where there is constant movement but smooth turns. It bothers me when the camera is slowly panning and half the screen is lagging behind throughout the whole movement.
When I'm slinging a gun around it all happens so fast everything is a mess of colours anyways, I'm not going to bother with the bottom half lagging behind.
Another feature I habitually disable to ensure higher performance is anti-aliasing. I play games at 1920x1080, I'm ok with the occasional pixel flickering if it means more even and higher FPS without micro stuttering.
My four year old rig can run most RO2 features at ultra this way, but on several maps I get horrible caching freezes when I enter new areas. This makes Countdown unplayable at times because spawning in a new area after each objective grinds the game to a complete standstill since the last patch.