Taking an extreme, stupid, recent example - Let's say the ad market has slowed down and you really don't need so many ad salesmen. And you decide to switch gears to a subscription model so you need to do some work in payments. But you have a hiring freeze.

Do you think the ad sales guys can help with the Square integration?

Or let's say you've decided to bet your social graph / web / mobile app centric company on VR. How many of those existing devs are going to be useful in VR if you have a hiring freeze? Or when you realize it's a debacle and scale down VR, how many VR devs are going to be good iOS app update churners? Etc.