Differences between PBIDesktop_x64 and PBIDesktopRS_x64 desktop tools

A question on the difference between the regular Power BI (PBI) desktop tool and the Power BI Report Server (PBIRS) desktop tool -

1. Other than the ability to both publish to the Cloud and save to Report Server, what are the differences between it and the standard PBI desktop tool?

I ask this because PBIDestopRS was last released at End-October.  Why is it kept several months behind the PBI desktop tool feature set?   

Also, I've seen comments that it's "optimized" for the on-premises server, but cannot find any discussion what that exactly is.  We'd like to stay current to the latest (January) feature set, but will need to save to report server.  A dilemma. 

Can you direct me to a blog or individual that can answer these questions?   M. Cameron.  Thanks.