It is for overtravel adjustment. It stops the trigger after hammer drops.

I recommend taking the screw out, throwing it away, and forgetting that it ever existed.

Best case scenario with using it- you eliminate a little overtravel- not that big of a deal. If it were big enough of a deal, you're probably a bullseye shooter and the factory trigger isn't going to be good enough to use without a good workover by a competent smith anyway.

worse case scenario- screw is adjusted enough that the sear barely trips and drags on the half-cock shelf dmaging the sear and causing light primer strikes.

Worst case scenario- the gun happens to be your carry gun and the screw has worked its way backward enough to completely block the trigger and render the gun inoperable when your life depends on it.

Like I said before, take it out and forget about it, put it in a box for later if it makes you feel better. If you really feel the need to use this gegaw, locktite it into place.