Lets just make up some numbers

Imagine your screen refreshes at 100hz 10 ms per frame with a perfect sync your input will be delayed by that 10 ms.

But what if you ran 200 fps, 5 ms. Well now your input is only delayed by 5 ms because a frame is being drawn every 5 ms and your GPU will only be holding on to that newest frame created every 5 ms to submit to the monitor

This latency would be addative to any latency from mouse/keyboard to computer as well as your monitor's processing time known as input latency tagged as "Lag" in tftcentral reviews

This example Acer Nitro XV273 X review noted that particular monitor they could only estimate potentially 0.5 ms of input latency but marked it as 0 as the estimate was not an actual measurement and 2 ms of grey to grey response times giving it a total input latency of 2 ms. Whereas the average range one may see goes from 3 to 8 ms.

Also worth noting that processing time of 100 ms on a television isn't unusual and that's why TVs are generally not recommended for gaming use.