Let me start by saying I appreciate the fact that the admins can add people to plan and work licenses with out going to their WF Rep, it keeps it very easy. However I would like to see a warning pop-up to notify the user that they are able to incur more costs.
The idea would be when you add to a paid license role above the number of licenses already paid for, a pop-up would warn you saying something like:
"A paid license is being added, please click yes if you would like to continue. Click No if you would like to cancel."
The idea would not be to slow down the ability to add users, but just to warn you in case the budget doesn't allow for additional licenses.