Correct me if I am wrong, but this is my thought process--
1. Back up iPhones, download videos, movies, etc. on MBP (320G OSX 10.8.4)
2. Back up MBP on 2TB EHD.
3. Delete the now backed up .avi, mp3/4, etc.
4. Abracadabra... HD space opened for further downloads.
5. Repeat.