The SAP software licensing model is considered to be amongst the most complex and costly to manage. While many software vendors typically calculate their license fees by counting the number of active and inactive users, or by considering the number of servers and CPUs, use of SAP Named user licenses is based on access rights.

Roles determine access rights and depending on what the user can do within SAP will determine the license required.  Customers are required to allocate a license to a user in SAP, however, the license does not restrict their access rights. Often organizations can allocate incorrect licences, resulting in overspend if too high a license is allocated or unbudgeted expenditure in an audit situation.

SOURCE: certero.com