So, when should you actually start using feature flags?

hey everyone, im thinking about our release process and how to better manage new features, especially for our larger, more complex systems. weve hit a few snags recently with deployments going sideways because of a buggy new feature. im considering implementing feature flags more systematically. my question is, at what point in a project's lifecycle or complexity do you find feature flags become a necessary tool rather than just an optional add-on? are there specific metrics or indicators that tell you 'its time' to adopt this pattern? curious to hear your experiences and best practices.