SharePoint orphaned users are those accounts which had access to SharePoint at some point, but have since been disabled or deleted in Active Directory. From here it's a slippery slope to permissions devolving into an inconsistent, unreliable, and undocumented mess. This results in occasional silent failures, and orphaned accounts remaining undetected in critical systems. They clutter and confuse permissions management and it can be very difficult to find every occurance of them within your farm.
Simple Account Manager makes orphaned user management easier. One of the most common mistakes that IT groups continue to make is to not properly manage user accounts when employees leave the organization. SAM is a security tool that makes SharePoint account management simpler.
By finding and disabling inactive, orphaned user accounts, potential security vulnerabilities into the network are sealed. Orphaned accounts may be exploited to gain unauthorized access to sensitive company resources.