Record-keeping and maintenance is one of the biggest struggles for busy MSBs. When you have tens of customers at the counter, and you are trying to keep everyone happy, records can easily be misplaced, or worse, lost. How prepared are you for the auditor or reviewer who is coming to request those documents?
There are so many tools available to organize and maintain your records for the required five year period! Cloud services are your friend. Avoid having a hard drive crash lose most (or all!) of your records by storing them on a cloud that can be accessed from different machines.
Paper copies should be a thing of the past. Hard copies of documents and records can be misplaced, destroyed, or even stolen, presenting multiple levels of risk for your business and your customers. If you prefer to have something you can touch, it's highly recommended that you maintain digital copies (on the cloud, please!) of any documents that you have paper copies of.
Additionally, digital records are more easily searchable, saving you (and your auditor or reviewer) time and effort. When the auditor is charging by the hour, you'd be surprised at how helpful this is.