With GitHub Actions, a workflow can publish artifacts, typically logs or binaries. As of early 2020, the life time of an artifact is hard-coded to 90 days (this may change in the future). After 90 days, an artifact is automatically deleted. But, in the meantime, artifacts for a repository may accumulate and generate mega-bytes or even giga-bytes of data files.
It is unclear if there is a size limit for the total accumulated size of artifacts for a public repository. But GitHub cannot reasonably let multi-giga-bytes of artifacts data accumulate without doing anything. So, if your workflows regularly produce large artifacts (such as "nightly build" procedures for instance), it is wise to cleanup and delete older artifacts without waiting for the 90 days limit.
Using the Web page for the "Actions" of a repository, it is possible to browse old workflow runs and manually delete artifacts. But the procedure is slow and tedious. It is fine to delete one selected artifact. It is not for a regular cleanup. We need