Requires is sorta a strong word. As with so many things in life, the answer is "It all depends".
There are plenty of examples both with and without recontouring. The B-17 for one - fixed slots outboard for handling qualities, inboard LE scoops (oil coolers?) all without any obvious recontouring. But it was a pretty slow aeroplane, with many draggy protuberances.
It may be that if there's a top speed or specific range shortfall, recontouring may provide the extra efficiency to meet the spec.