By a default MAS installation, the MAS service itself runs as the built-in local account SYSTEM and the COM+ application runs as MASService. MASService is a local account on the computer created by the installer. Those accounts will both have admin rights to the computer. The MAS service itself is the scheduler of jobs while COM+ application pool is the worker process that performs the execution of the analysis configurations, data configurations and etc.
The MAS service and COM+ application identity need to be configured to run as a domain account instead of the default local accounts, when the scheduled tasks involve elevated permissions, such as accessing a shared file location.  See this Microsoft article about domain user accounts for more information: https://docs.microsoft.com/en-us/windows/win32/ad/domain-user-accounts

Note : The windows domain account that MAS is configured to use, should preferably be a service account whose password does not expire. The service account should have administrator privileges on the MAS server, as it spawns other child processes to parallelly run scheduled tasks and have the ability to create temp files as the jobs run.  Please ensure that the service account should also be configured to have access to any shared drives, if any are used in the scheduled tasksets.

• https://docs.microsoft.com/en-us/windows/win32/ad/domain-user-accounts