Can someone tell me exactly what it does?
The difference between it on and off is STAGGERING, with a 60 fps difference from my experience.
What on earth could this do to improve performance so much? I know it has something to do with input, however going from having it on to having it off, the whole game suddenly just felt sluggish.
It has nothing directly to do, with input (directly). One frame interval allows your CPU to calculate the next frame, while your GPU draws the previous. When it is off, your CPU has to wait till the GPU has finished drawing, before it is allowed to calculate evereything for the next frame frame.
To illustrate
OFI off.
CPU draws for 8 ms (Frame 1) after that GPU draws for 12 ms (Frame 1) after that CPU draws for 8 ms (Frame 2) after that GPU draws for 12 ms (Frame 2) and so on. resulting in 20ms per frame.
OFI on.
CPU draws for 8ms (Frame 1) after that GPU draws for 12 ms (Frame 1) while CPU draws for 8 ms (Frame 2). GPU draws for 12 ms (Frame 2) while CPU draws for 8 ms (Frame 3). resulting in 12 MS per frame after the intial frame.
Because your CPU is the one working out input. It has already done all calculations a bit sooner than before, which means that the frames are calculated with older input data. However keep in mind.
OFI only calculates 1 frame ahead at most. There is no runaway effect.
The inputlag it generates is frame dependend i.e. fewer FPS higher input lag since OFI increases FPS it partially offsets the negative by providing overall faster updates of your gameworld.
My personal view is to keep OFI on at all times. You could propably have it off, when you reach your desired target FPS without it. But at 144 fps, I would argue the inputlag it might generate is very low anyways.
If you get high enough frames it’s worth having on because the delay it does give you is so tiny in comparison to the fps loss of having it off. If you don’t get high enough frames you need it on or you don’t get enough frames.
Unless you have a complete beast of a machine that’s getting 144+ and never dropping with it off, don’t turn it off.
This is correct, you get like 7ms of input lag at 144fps and 16ms of input lag at 60. Funnily enough the higher your frames the less it matters that it’s on, and it gives higher frames to have on.