What's the difference between mouse accel and mouse smoothing?

[Nejco]

^

[Air]

Mouse acceleration changes cursor travel distance based on the movement speed of the mouse, mouse smoothing, on the other hand, is pretty self-explanatory, it just interprets mouse movement to make it move more smoothly but adds a slight delay to the mouse, it was made more for older low-DPI mice.

All in all, neither option is really worth touching when it comes to gaming.

[Bad 💀 Motha]

AIR explained it well enough; PC Gaming = disable both of those.
If you do not have an on-the-fly DPI changing mouse, then after disabling both of these features, then adjust your in-game sensitivity more to your liking for you and the particular mouse u have at that time. And each game will be a little different feeling as far as sensitivity goes.