If you really want to know, read Sec. 11.4 and 8.4. If you don't, we strongly recommend the following: If you are currently taking scans with STXM 5 and dealing with the files you recorded just shortly ago (during this run of beamtime), you should open from and save on the server. This gives you access to the microscope control computer's data directory.
If you are dealing with files which you have on your local hard drive, or on a CD / DVD (like older data files), open and save them locally.
If you run SM_GUI in display_only mode to process previously recorded data files, the "on server" options are disabled anyway.