Clearpass is pretty easy on licenses..
It works with rolling periods but ease I'll pretend they use weeks and months (where normally its riolling 7 and 30 day avg).
If your 7-day rolling average exceeds your license count that month will be marked as "license exceeded".
If you get 4 out of 6 consecutive months license exceeded clearpass will take action and start locking you out of the administrative interfaces.
That means all your dot1x authentications and such will keep working. However you can no longer edit config or even create guest users.