I like how one of the oldest concepts in programming, the ifdef, has now become (if you read the press) a "revolutionary idea" created by Facebook and apparently the core of a company's business. I'm only being a little sarcastic.
This is more than just the technical capability. I've been on teams that insist they are completely unable to iteratively develop and deliver big features. As a result you end up with huge impossible to review patch drops at the ends of months of work behind closed doors. It's a disaster every time.
I'm still struggling to communicate to people how to do it and what the benefits are.
But the real power behind the idea is not the ifdef piece, it's the idea of dynamic, context-aware configuration. You've got a user-friendly tool that can control the code paths being executed in your application without restarts or redeploys.