This article walks SharePoint site administrators through setting up classic retention policies. Retention policies can be used to clean up documents or even versions.
Without recurrence selected, the retention action will be executed on an individual document only once. If the document is being deleted or moved to recycle bin, no recurrence is needed. However, if you want to repeatedly check documents for previous versions (and your document is always being updated) and delete all previous versions except the last, then you may need to check Recurrence. Otherwise, after an initial run, previous versions will start to pile up again.
Microsoft controls the schedule of the timer job that kicks off retention policies. The job usually runs once per week over the weekend. This means, that the retention action may not kick off on the exact date the time period expires so don't panic if you still see documents after the time period specified in the policy.