This information is used to display file availability informations. You should therefore always try to keep the state of all your MyList entries up to date.
For the moment the following Filestates are available:
The unknown state means that you are not specifying any availability data for that file. This is the default value.
internal storage (HDD)
You have that file on your harddrive.
external storage (CD/DVD/...)
You have that file on CD or DVD+-r (no video DVDs!).
You no longer have that file but want to keep it in your MyList never the less, i.e. to keep a list of stuff you've watched (otherwise just delete the file from your MyList).