Feature flags in a multi-tenancy application

A scenario for having long-lived feature flags is in a multi-tenant application where the same codebase serves multiple projects - e.g. a multi-site Drupal application or a module reused on multiple websites.

This is the use case I have for a client project which uses a multi-site setup to serve multiple websites from the same Drupal codebase.

If I need to add a feature to sites 1 and 3 but not site 2 or test a change to only site 2, I can do this by enabling a per-site feature flag.

Instead of being removed, these flags will remain until the change can be made permanent on all websites, meaning it can be toggled on and off as needed - allowing each site to be configured separately whilst keeping it easy to maintain by having a single canonical codebase.