As a Jira administrator, I frequently see this problem: child issues are closed but nobody remembered to close the parent issue. Users have already moved on to the next thing and the parent issue sits in its incorrect status forever. Or maybe it's the opposite: the Epic is closed, but its Stories, Bugs, and Tasks were forgotten.
When issue status does not reflect reality, reporting is a nightmare. All completed or unneeded issues should be transitioned to their final status. Why not take this step off your user's "to do" list and automate it? It's easy to automatically transition issues with Innovalog's Jira Misc Workflow Extensions (JMWE) app.
Use Case: When all child issues are closed, automatically transition the parent so users don't need to do it manually. Example: When all Sub-tasks are transitioned to the "Closed" status, automatically transition the Task issue to the "Closed" status.