Let's say you are at 250 knots and suddenly given a shortcut. Should you stay at 250 knots with the speedbrake until you level off, then reduce speed and confirgure, or reduce speed first, configure, then descend as quick as you can??
Go down then slow down. Keep your speed at 250kts, SPDBK out. Level off then reduce speed. The air is thicker low down therefore total drag is higher and the TAS is closer to the IAS thus the distance required to decelerate will be less.