Ok, I did some quick testing and here is what I found...
1. if you install the ALM temp license when installing ALM, and that license expires, the ALM portions of the license expire but the PC license portion does not and when a users logs in they will pull a performance center license and have access to the Testing module. They will not be able to access any other modules.
2. Once you have a valid license installed then users will pull a qc license when logging in until all are used up.
3. If you create a group and go into module access and remove access to all modules (you will get an error when you try to save these changes) when a user in that group tries to log in they will get an error that they cannot access any modules and will not be allowed to log in.
4. If you remove access to all modules except for Lab Management then when that user logs in they will receive a PC License. This only gives them access to Test Lab and Test Runs under the testing Module.
So if you are looking for a way to keep Performance Testing user from using a full license you could try #4 above. The reason that it works this way is so that even if all the ALM licenses are in use you can still run Performance Tests if you have the Performance Center licenses installed.
I have been asked in the past if users pulling this PC License violates the license agreement and was told no by HPE at the time.
Scenario #4 above was the only way that I found that you could force a user to pull the PC license unless all ALM licenses were in use.