It controls the amount of pressure required to blow off when they are locked out I think. If you wind it all the way clockwise +ve then back it off about 2-3 turns give that a whirl. The more you back it off the more sensitive to bumps it is, well thats what I've been told anyway. Only done about 40 mile on mine so hard to say yet.
Basically yes, but not just when they're locked out (despite what the manual says)
See Kapusta's description here : linky
(I run something inbetween 2 + 3 - very little brake dive/squirming when cornering but fully active over bumps)