Here's a small but extremely important little feature that's been added for developers in Google Play. Should a bug be found in the middle of a staged rollout, you can immediately halt said staged rollout to keep the bad code from hitting any additional devices while you work things out.
In other words, an emergency brake. It won't roll things back for those who have already received the update, but it'll keep anyone else from downloading it.
That's not to say that we don't get that staged rollouts can be a little frustrating for the user — there's nothing more annoying than hearing that a cool new feature is coming ... eventually. But even worse is when you know you've pushed bad code and can't do anything about it. This is a good addition for devs.