You can monitor and analyze the actual usage of Salesforce user licenses in your organization using a variety of usage reports available in License Statistics. In addition, there are other usage details you can check to get an even more detailed picture of how many Salesforce licenses you have in your organization and how they are being used.
License Statistics allows you to monitor the following Salesforce license usage information:
A list of users that are currently logged into Salesforce during any period that usage is tracked (active user sessions).
A list of all users available in the Salesforce database.
Note: Due to its experimental status, monitoring Salesforce licenses is disabled by default. If you are interested in the feature, please to obtain a simple instruction on how to enable monitoring of Salesforce user licenses. This will allow us to see how many customers show interest in using this feature.
We would like to encourage everyone interested in using this feature to try it out and let us know about your experiences: the good, the bad and (maybe) the buggy.