Think of the end goal. That is to arrive on the end of your approach, gear down, flaps set at the required speed with an appropriate power setting. Your starting point is in a descent at say 250 knots with idle power. In an ideal world you will slow the aircraft up, lower the flaps stage by stage, lower the gear, lower the rest of the flaps and then set approach power. The tricky bit is to determine your initial descent point which may have been 140 nm away.
The problem is the real world. Your have to share the sky with other people and comply with sometimes ludicrous ATC constraints. This generally means that idle descents are impossible. When in such a system, I fly my plane as clean as possible (less drag) and only lower flap to enable a lower speed. I try not to use flaps to slow down but there are times when you have no other choice.
PM