MCAS is bound to the information provided by MDATP or any other network appliance (SWG, Firewall and etc.).
You are able to monitor the app's usage patterns such as the number of users using the apps, the amount of data being uploaded and downloaded and etc.
By using the Sanctioned/Uns-anctioned tag, you are then able to set automated policy-based alerts to be notified when a certain app's (in this case Gmail) usage patterns violate company regulations.
We are planning to provide visibility into file hashes that are being uploaded to any of the monitored apps and protect sensitive data upload to Risky/Un-sanctioned apps. No ETA yet.
More information can be found here:
I suggest taking the AIP/MDATP question in MDATP forums.