If you are pushing a constant 120 fps or 144 fps if your monitor supports 144Hz ULMB, you should give ULMB a try. ... If you are playing the latest games and your frame rate is all over the place, we would recommend you stick to G-Sync mode as it will prevent screen tearing.

What is ULMB good for?

Ultimately, the main purpose of ULMB technology is to keep motion blur to a minimum, so it is a useful technology for situations where that is a top priority, such as competitive gaming.

Which is better G-Sync or ULMB?

Motion blur is practically non-existent in the ULMB setting as compared to the G-sync setting. In my case, already achieving high FPS in-game, the smoothest, clearest game play is ULMB as the victor over G-Sync. I average 145 fps or so with my current settings.