Welcome to A/B rollouts.

The idea is that instead of making a sweeping change for every single user, you roll a feature/system/UI update, etc out to a small number of users, to see how effective it is. It gives you time to see how those users react to it, how they interact with it, how it impacts their broader site usage, etc… And then once they have had time to gather some feedback and work out the bugs, they push it out to the rest of the users.