I only knew the folllowing after I launched the program and it started copying my whole music library (8.42 GB) to a new folder it had created in the "Application Support" folder in my User Library. I figured it was doing so, because I could hear my Mac chewing on something. It was only after hearing this and watching space of my hard drive disappear one GB at a time, that I read the following in the help files iTunes Switcher installed on my Mac:
To save hard drive space, especially with large collections, you may wish to go into iTunes Preferences, in the "Advanced" tab, and deselect the option to "Keep iTunes Music folder organized." If you allow iTunes to organize your music, then the process of duplicating your library will also create duplicates of your audio files, doubling the amount of space they take up on the disk. On the other hand, if you organize your collection manually, anywhere outside of the "~/Music/iTunes" folder, then the files will not be duplicated by iTunes Switcher."
I would suggest using Libra instead:
and the develper's site, which has a helpful explanation of the difference between Libra and iTunes Switcher: