What effect does the leading edge slot in the aircraft wing have on

Slots may be found placed slightly aft of a wing leading edge , between a leading edge slat and the wing leading edge or between

I was referring to a pivoting fixed slat that has a fixed amount of travel so that at its farthest point away from the wing the exit area is roughly 13 or less

fixed slot leading edge Slots In contrast the McDonnell Douglas F-15 has a fixed leading edge because of the type of airfoil used for

noble sky slot Has anyone ever put a wing leading edge slat or a fixed slot on a Cessna wing? There must be thousands on mods for these planes but I have