Daydream,
The primary value for me, is that in the event of a loss of the mc database (something that has happened 5 times in the years ive been using it, though never the fault of the software) I still have all of that data. I enter a huge amount of metadata for each file, and they move around alot. music is great, i just reimport it, and theres all my data. but for movies and TV, i enter Director, actor, plot synopsis, info on how i encoded the file, etc.. once you do that for about 100000 files, you really dont want to have to do it again. now, in that terrible event, i dont have to depend solely on having a good backup of my DB (even then if its 5 days old i loose alot of data). worst case it gets loaded from the sidecar. second i can move a vid file to another users system with the file and all my inf goes with it!