I managed to destroy my Authenticator keys and just got re-enabled by Coinbase.  So, any time that I had been asked for my Authenticator code it would fail.  So, I could not access Coinbase or Coinbase Pro on my phone, but could access both on my tablet, and could only access Coinbase Pro on my desktop.  If any of these would have had occasion to ask for my Authenticator code it would have failed and then I would have no longer have had access.  I can still access other exchanges that use Authenticator codes.

So, my question is under what circumstances is one asked for an Authenticator code?