Content cleanup means purging it of unnecessary items and appropriately archiving the ones that are necessary to your business. Doing so allows you to reduce your overall unstructured data footprint -- i.e. leaving you with less junk and stale data to distract you, as well as less sensitive data to protect, thereby reducing the overall risk posed by your unstructured data.
KRM's "Information Governance: A Practical Guide" offers a methodology that you can use to implement information governance in your own organization, toward the “active and controlled handling of data and information."
In addressing the problem of over-retention of electronic information, day-forward information disposition is easier; disposition of historical information is the tougher nut to crack. Part 2 of Rich Medina’s tips on how to go about it.