It is not rare for large organizations – or even smaller ones, to lose track of internal TFS adoption and MSDN usage.
Do you want to do an internal audit of users of TFS and also Visual Studio users? Do you want to determine a shortfall (or overage) in TFS CALs and determine who is accessing TFS and would need Visual Studio or Test licenses?
We have built a licensing page in TFS Web Access for 2012 to help companies self-audit. You can assign people the sets of capabilities you think they should have and others will be hidden from them. If they ask for access, you know you are under licensed :)
The three license levels are Limited (equivalent to Work Item Web Access), Standard (equivalent to a CAL or any product that includes a CAL) and Full (equivalent to Premium, Ultimate or Test Professional).