Use this location to save a file relative to the preferences folder. Useful for per-user files that are across all projects.
Location of the Preferences folder across operating systems:
Windows: C:/Users/[username]/AppData/Roaming/Unity/Editor-5.x/Preferences/
OSX: /Users/[username]/Library/Preferences/Unity/Editor-5.x
Linux: /home/[username]/.config/unity3d/Preferences/Editor-5.x.