[Theohazard]

"Prepping" the trigger by beginning the pull before you're fully in the shooting position doesn't have to contradict the "finger off the trigger rule". In the Marine Corps I learned it the following way: "Keep your finger straight and off the trigger until you intend to fire". For me, as long as the gun is pointed at the target and you actually intend to shoot, you can put your finger on the trigger even if you haven't yet established sight picture.

Some instructors teach the following technique: Draw the pistol into the ready position, and while you're driving the gun forward to the target your finger is on the trigger and you're removing the take-up and preparing to fire as soon as sight picture is established. During this process your finger is put on the trigger while the gun is still close to your body in the ready position, but the gun is pointed at the target the entire time your finger is inside the trigger guard.

This technique could definitely cause problems for someone without enough training or practice under their belt, and it also could cause problems for someone who pulls a gun but doesn't intend (or isn't justified) in firing it. But for me, I will never draw my gun unless I intend to use it at that moment and am fully justified, so it's a technique that I practice.