Bypasses your windows mouse settings and makes it so that your game movements read directly from the mouse instead

Some windows settings cause accel so if you use rawinput you can use whatever windows settings you want without it effecting your game.

Having it off imo makes it easier for you to develop muscle memory for mouse-to-ingame movement. With it on, you'd have to learn the direction, distance, and speed, and with it off you'd only need to memorize the first two. Granted, that's only if you haven't turned off your OS / mouse hardware / driver acceleration.

Tbh it really doesn't matter too much, there are players who swear by it and can't play with it on and those who feel as if their mouse is too heavy w/ raw input on.

i use 1800 abyssus dpi, set windows to 4bars so i can actually control the mouse while it still being not slow as fuck 450

by having raw on I avoid having windows sens affecting my ingame while still affecting dota/etc to keep things consistent