It hosts reusable workflows that other repositories can call to run consistent CI jobs (build/test/lint/release/deploy) without duplicating YAML across (too) many repositories.
It guarantees:
- a single source of truth for CI logic,
- consistent defaults (runners, caching, permissions, artifacts),
- safer changes via versioned tags (
v1,v2, ...), - lightweight per-repository workflows (just a wrapper that calls the shared workflow)