It alters the frequency with which a kickout hole is lit for special, once that column of numbers is completed (i.e., the four different 1-4 sequences). All four numbers are still needed for each column.

For 5-ball play, the recommendation is for conservative, and for 3-ball play, liberal (IIRC).

(I'd have to go back and look at the schematic to recall exactly what it's triggering off for the frequency.)