The Curious Case of the iPod Photo Cache

This morning I logged-on to find that I had an extra 20GB of free space on my hard drive! Comparing my Mac HD to my CCC backup, I traced the discrepancy to the iPhoto Library (i.e. the backup file was 20GB bigger than the today's version).

Then I opened the backup iPhoto and compared it to today's. Everything was the same: same number of events, same number of photos, and same number of photos in Trash.

Then I clicked on Show Package Contents for both versions of iPhoto Library and the culprit was a sub folder called iPod Photo Cache – which last week was 20GB in size, and is now just six MB.

So I'd like to ask: Does anyone know what just happened? Or what the iPod Photo Cache is? My instinct is to be wary. Is there anything I should do? Or should I just be happy with my extra 20GB.

btw I haven't used an iPod for years and I never stored photos on it.