I can think of at least one good reason for putting
movies,
mp3s, etc. in a
.zip archive. Correctness.
Quite a lot of compression formats (
mpeg,
realplayer,
mp3, etc.) will fail
silently if they become
corrupted, or shortened, the errors showing up as blips in the audio, or
artifacts on the screen. Or even just the tail end of a song going missing.
A
zip file, on the other hand, contains information on the expected filesize, and
CRC for each file. If the
archive becomes damaged you'll know about it. And if you don't want it in a zip, you can take it out again. A processor capable of playing
Divx, or mpeg video can easily cope with unzipping a file, and packages like
zipmagic make the process transparent. For a minimum of inconvenience, you gain a lot in data security.
And it might even save a few
bytes, too.