When is Auto Focus?

In the Auto Focus Options window the 3rd from the bottom checkbox says, "Auto focus before sequence start (not on resume). The help file for this option says, “Auto focus before first frame: When checked this will auto focus before the sequence starts (not applicable to “resuming a sequence”).”

If this box is checked and “Auto focus after automatic centering action” is not checked, will auto focus be performed only once at sequence start? Or, will it be performed before the first frame of each target?