Having a distributor "LOCKED OUT" simply means you have all your advance in it (say like 38 degrees) at an idle. There is no vacuum advance or centrifugal advance at all, they are "LOCKED OUT" or disabled mechanically.
< The reason behind it is that in a full race motor like in dragracing you dont want to wait for a advance curve to come into to play, you want instant throttle response and imediate engine excelleration since 99 percent of the time your at WOT anyway. There is no need for a distributor with a advance curve like in a street machine where your on and off the throttle contionously or at part throttle cruising around,
so you lock out all the advance mechanisims, and just set your distributor at full advance. Usually used in conjunction with some sort of start retard or by seperating the cranking and ignition circuit to help ease starting difficulties in a fully advance engine.
Cp