If you are talking about 1 LSN screw it will adjust the mixture adjustment at lower rpm, in normal words it will adjust the acceleration.

If you are talking about 2 screws (1 brass color in the housing of the carb and 1 in the slide) then both do the same. Adviseable is to keep the large brass one equal to the housing and just use the one in the slide.
If you screw in the one as much as you screw out the other one the adjustment stays the same but you did move the spraybar to another spot in the airflow what can result in a beter result but it can also get worse....