Seed data powers demos, tests, local development, and static catalogs. It should be clearly separated from live user data.
ELI5
Think of Seed Data as a labeled box where an app keeps important things. Starter data loaded into an app so it has useful content before real users arrive.
In practice
Use it when a feature reads, writes, migrates, validates, or audits stored information. In practice, define the owner, input, output, and failure mode before you rely on it.