When hive.server2.enable.doAs=True , HiveServer2 performs the query processing as the user who submitted the query (usually the user you kinit with, it could be service account or an account assigned to a team ). But if the parameter is set to false, the query will run as the user that the hiveserver2 process runs as, mostly Hive
This will help to :
1-Better control the users via Hive Ranger policies
2-Better control the ACLs mappings for Yarn, so you can assign every user on a specific Queue.