At my company we have Server, Portal and Data Store services running with a Windows domain user account who's password does not expire (Enterprise 10.6.1). Our company is implementing a policy where these types of accounts will get a new password very frequently (possibly daily). Will this require us to either run the utility ('configureserviceaccount' or 'Configure ArcGIS Server Account utility') to update the password every day or switch to a local account? Or will these Enterprise systems recognize that there's a new valid password (since it is in fact not expiring, but being constantly changed)?
If the password to the account used to run the services changes, you'll only run into a problem if the service is stopped and then you attempt to start it. Since the password is invalid, you'll receive an error. As you guessed, you'll need to run the utilities to update the password or use a local account whose password won't change.