a polite way of requesting a hand-holding walkthrough of something for an idiot
Comes from aviation. When a plane lands at an airport, the tower usually gives the pilot directions to his gate. If the pilot can't remember the directions he can request a progressive taxi, where the tower guides the pilot to his gate (turn left... go straight 200 yards... turn right). This is a nuisance to the tower because it requires that someone usually focused on difficult job of directing traffic in the sky to divert their attention to something stupid like giving simple directions on the ground.
Store clerk 1 to clerk 2: this gentleman needs a progressive taxi to the mens shoes section
store clerk 2: Got it. Come with me sir, ill show you where they are.