Beagle quotes the standard RAF method as taught by at least one well respected FTO teaching FIC. If the aircraft is at the correct height when full flap is taken there should be no problem and I suspect the SOP originates from the same stable.
My experience of PPL students who may not roll out on finals at the correct height, leaves me a little cautious and I have always adopted the technique of teaching selection of (land) flap when its safe to do so.
Power controls rate of descent, pitch controls airspeed
It can do, but its much more efficient to hold the required attitude with pitch and maintain speed with the throttle! Holding one of two variables constant, only leaves you with one variable to correct for. The RAF required us to teach this method on Flying Scholarships.