This article was helpful. It's a nice primer on ID management.

The core objective of an ID management system in a corporate setting is this: one identity per individual. But once that digital ID has been established, it has to be maintained, modified and monitored throughout what has been called the "access lifecycle." So ID management systems provide administrators with the tools and technologies to change a user's role, to track user activities and to enforce policies on an ongoing basis. These systems are designed to provide a means of administering user access across an entire enterprise and to ensure compliance with corporate policies and government regulations.