You asked what its for, the original post says it changes fps and reaction time. However;
"With reaction of 2000, it will take bot up to 2 seconds to notice that a new npc, object, etc has been spawned/died/etc.
Fps setting affects other data refresh rate (such as opened interfaces, npc hp, etc).
So with 50 fps, it will take bot up to 20 ms to notice that a new interface has been opened, npc hp has changed, etc.
With 20 fps, it becomes 50 ms; With 10 fps - 100 ms and so on..."