Microsoft Knowledge Base Article 824196 contains the following summary:

License Logging Service (LLS) is a tool that was originally designed to help customers manage licenses for Microsoft server products that are licensed in the Server Client Access License (CAL) model. LLS was introduced with Windows NT Server 3.51. By default, LLS is disabled in Windows Server 2003. Because of original design constraints and evolving license terms and conditions, LLS cannot provide an accurate view of the total number of CALs that are purchased as compared to the total number of CALs that are used on a single server or across the enterprise. The CALs that are reported by LLS may conflict with the interpretation of the End User License Agreement (EULA) and with Product Usage Rights (PUR). LLS will not be included in future versions of the Windows operating system.

For example, when you use the Licensing snap-in (Llsmgr.msc) to view the purchase history of product licenses, the Purchase History window may be blank or inaccurate. However, when you access the purchase history from another server computer, the purchase history may be correct. You can add new licenses, even on computers where the purchase history is inaccurate.