An overview of the different web-based administration portals and PowerShell connection methods for administering Office 365 services.
Saving Credentials for Office 365 PowerShell Scripts and Scheduled Tasks
PowerShell functions for securely storing and using credentials that can be easily re-used for authentication in scripts and scheduled tasks.
Exchange Best Practices: Least Privilege Administrative Rights
When it comes to Exchange Server the the principle of least privilege applies, and is considered a best practice.