Everytime you sign onto a new screen you log in with your credentials. Then its set
if more than 5-6 at once then it kicks someone else
then you send a text chain to kick someone out. But very unlikely that happens
But if they are like Neflix who just started this, soon you will not be able to switch anymore
In the beginning with their new setup, when you login to your account at another location, the first 2-3 times it asks you and allows you to change your home location
Then it won't let you anymore eventually
Not saying youtube does this but in what Tanko posted it does say sharing must be in the same household, so maybe that's just a scare tactic or they will actually have the IP tracking on device(s) like Netflix now