Resource check
scripts in Concourse will emit the most recent version of a resource by default. For example, configuring a git -resource in your pipeline to point to a git repository's master branch will emit the latest commit SHA as the version.
For some resources, (eg. the github-release resource) you may not want to use just the latest version emitted by the check script; you may want an older version of that resource that isn't the latest one at the time of configuring your pipeline.