On windows systems is recommended to have principal folder referenced as "My Documents" under "Documents Library"
One important consideration on this regard is that depending on Windows version, physically this folder can be located at:
or similar locations. And this path is the one to be used on maintenance processes like backup and synchronization.
If you use other Operative System identify the physical location of your files in order to be sure where to copy your files to external locations when required (i.e. backup processes)