Diminishing returns as you go higher and higher.
144fps/hz is 6.9ms per frame. 240fps/hz is 4.2ms per frame.
Assuming you can actually output 240fps consistently, you'd be getting a 2.7ms reduction over 144.
60fps/hz is 16.7ms per frame. 75fps/hz is 13.3ms per frame. Which is a 3.4ms difference between the two.
Only a 15fps difference between 60 and 75...yet more of a frame time reduction than going from 144 to 240. You get the idea?
You'd literally notice the difference between 60-75 MORE than 144-240, despite the latter technically having almost 100 extra refreshes per second over 144. And theres the matter of your PC being able to output that many frames, and the increased heat/power/noise from doing so.
You can draw your own conclusions from this, obviously. But i'd save the money and get a much nicer 120hz/144hz monitor instead. Or if you already OWN a 144hz monitor...buy something else.