I am planning to upgrade my Tableau instance from 8.0.x to 8.1.x (New-machine Upgrade mode).
In the Pre-upgrade check-list: It was indicated that the account was the one that was used for previous Tableau server version.
Confirm that you have the user name and password for Tableau Server’s Run As account.This is the account you configured Tableau Server to run under when you installed the earlier version of Tableau Server. You can view the Run As username by clicking Start then navigating to All Programs > Tableau Server > Configure Tableau Server.
I have to change the "run as a service account" for the new machine I would be upgrading to for compliance issues.