As shown in the Installation section earlier, a PowerBIDesktopRS_x64.msi file is also available for download from the MS Download center. This is the application used to create Power BI reports to be published to this version (October 2017) of the Power BI Report Server.

As shown in the following screenshot, this application can be distinguished from the standard Power BI Desktop via the title bar (here, October 2017) and the Save As menu: 

 

As suggested by the Save as menu in the preceding screenshot, a report created via the Power BI Report Server optimized application can be saved directly to the report server. In other words, a PBIX file doesn't necessarily have to be saved to a user's machine—the Power BI Report Server can serve as a network file share. If a report needs to be modified, the user (with a Power BI Pro license), could open the file directly from the web portal described in the following section and save their changes back to the report server.

At some point in the future, a single version of Power BI Desktop that can be used for both the Power BI service and the Power BI Report Server may be released. This has been identified as an important goal that Power BI teams are currently working through, though no timelines have been suggested as of this writing.