With computed folders, such as you may use with multibranch plugins (like github or bitbucket branch source) and a "git flow" way of working, you tend to create a lot of short lived branch jobs.

These branch jobs are removed not long after creation (as pull requests are merged) and the job removed, however the workspace on any nodes can live around for up to a month before it is cleaned up by WorkspaceCleanupThread (https://github.com/jenkinsci/jenkins/blob/master/core/src/main/java/hudson/model/WorkspaceCleanupThread.java#L115)

I am proposing that in the removal of orphans a similar scanning and removal of workspaces could take place. This can supplement the cleanup thread and make for less garbage filling up disk.