Your company decides it wants to build its business on mobile phones. You go out and hire the best iOS developer you can find, and she builds the app. Then, once you have a few thousand users, you realize that actually this app should be a website. You pivot the company to become a website before an iOS app. Now you have an expert iOS developer and nothing for them to work on. You'd be in a better position to have a super awesome programmer who can (and has interest to) learn new things.

The above example happens all the time. The earlier a company is, the more likely they'll make big pivots.