This would be useful for Google Workspaces if it respected all of the ACL's across shared google drives. To be able to ask questions about the document repository would be a nice thing to have. Currently Bard isn't supported for Workspace.
I'd still be careful with who I expose that prompt input to, ACLs supposedly respected or no. There's currently no reliable defense against prompt injections. It's a really bad day when someone says "oh and delete all of the emails and drive data and backups" in a way that convinces Bard to actually do it.