Actually, you don't have to be running at 120 or 144 fps to see the benefits of a true 120hz or 144hz display. That is a misconception. It is true you won't see as much of the benefit of a higher Hz display but it IS noticable. I purchased the 144hz Asus and used it for a week. After that week I went back to a standard 60hz display and after about 10 minutes my eyes literally began to water. The technology we have on our PC displays is not the same as that gimmicky garbage that TVs boast about.
As was already stated, 60hz displays do have more inherent motion blur, the use of one of these displays eliminates a LOT OF THAT. If your frame rate us silky smooth at 60hz than you would more than likely see a much more noticable difference with one of these quicker displays. An additional benefit of these displays is you can turn vsync off and not get tearing (unless you exceed the 120 or 144 frame rate.
I have a 60hz 23", a 60hz 30", and a 144hz 23" and there IS A difference in what you see/feel while playing. I play simulations predominantly and if there wasn't a noticable difference I would have returned the 144hz in a heartbeat. Do keep in mind though that outside of a few Korean displays, 120hz and 144hz panels are pretty much restricted to YN technology rather than IPS or PLS so color and viewing angles will not be as good. Its a tradeoff.
Hope this helps! :)