Windows Small Business Server 2003 Standard Edition includes Windows Server 2003 and Exchange Server 2003 technology. You get the capabilities of a security-enhanced small-business network with storage printing collaboration e-mail Internet connectivity support for mobile workers and faxing.
In Per User mode a separate CAL is required for each user that accesses or uses the Microsoft Small Business Server 2003 software on any server. You may reassign a Windows CAL from one user to another user provided the reassignment is made either (a) permanently away from the one user or (b) temporarily to accommodate the use of the Windows CAL while a permanent user is absent or by a temporary worker while a regular employee is absent.
By having two types of Windows CALs you are able to use the model that makes sense for your organization.