I have found feature flagged rollouts to be one of the biggest advances in fairly recent software development. Probably too much to say about it in a comment, but they massively de-risk launches in a number of important ways, both in being able to quickly turn a feature off if it has unintended consequences and being able to turn it on for a very specific set of users.

With that said, I think that LaunchDarkly and the like are a bit expensive and heavyweight for many orgs, and leaving too many feature flags lying around can become serious debt. It totally makes sense to start with something lighter weight, e.g. an env var or a quick homegrown feature in ActiveAdmin.