Hey Fancois!
What is included in Full Cloud Integration?
Firebase is deeply integrated with Google Cloud Platform.
Every Firebase project is also a Google Cloud project under the hood. When you upgrade to the Blaze plan, you can use any of Google's world-class Infrastructure-as-a-Service directly inside your Firebase project, at the same low prices as Google Cloud (for equivalent features).
There are many security-enhancing, latency-improving, and time-saving benefits to using Google Cloud with Firebase (versus other, non-co-located Cloud services). Many of your settings are shared between both services, including collaborators and billing information. All your Firebase and Cloud usage appears on the same bill.
So, mainly, this just means that billing is integrated between the two. You are correct in that you are able to use the free tier GCP products for all non-Blaze plans. We realize this answer is a bit hidden and several team members were talking about how we can make this clearer earlier today.
Cheers,
Jacob