"VM instances that only have internal IP addresses (no external IP addresses) can use Private Google Access.
They can reach the external IP addresses of Google APIs and services. f you disable Private Google Access, the VM instances can no longer reach Google APIs and services; they can only send traffic within the VPC network."
https://cloud.google.com/vpc/docs/private-google-access

The above is a real world example of a company named Planet, where they sent around 80+ satellites to take pictures of earth every day, 24 hours. They run around 40,000 preemptible VMs concurrently.
Preemptible instances function like normal instances but have the following limitations:
Compute Engine might stop preemptible instances at any time due to system events. The probability that Compute Engine will stop a preemptible instance for a system event is generally low, but might vary from day to day and from zone to zone depending on current conditions.
Compute Engine always stops preemptible instances after they run for 24 hours. Certain actions reset this 24- hour counter.
Preemptible instances are finite Compute Engine resources, so they might not always be available.
Preemptible instances can't live migrate to a regular VM instance, or be set to automatically restart when there is a maintenance event.
Due to the above limitations, preemptible instances are not covered by any Service Level Agreement (and, for clarity, are excluded from the Compute Engine SLA).
The Google Cloud Free Tier credits for Compute Engine do not apply to preemptible instances.
Reference link- https://cloud.google.com/compute/docs/instances/preemptible

Policies are a union of those applied to resources themselves and those inherited from higher levels in the hierarchy. If a parent policy is less restrictive, it overrides a more restrictive policy applied to the resource. If a parent policy is more restrictive, it does not override a less restrictive policy applied to the resource. Therefore, access granted at a higher level in the hierarchy cannot be taken away by policies applied at a lower level in the hierarchy.

Explanation
Cloud Debugger is a feature of Google Cloud Platform that lets you inspect the state of an application, at any code location, without stopping or slowing down the running app. Cloud Debugger makes it easier to view the application state without adding logging statements.