They're not always booleans - for example, we often see feature flags being used for A/B rollouts.

Cloudflare themselves even uses them internally as such, by shipping new features/builds to their free customers first, and then progressively larger customers after a settling period.

Feature flags can also be randomly turned on, for a sort of fuzz testing. Don't think of them just as 'new things' - it could be 'changed behavior'.

I guess you could think of them as a boolean on every client but they're generally not implemented that way.