COW is great. It has applicability around on-disk consisteny, and it makes snapshots much more coherent. It's also not without downsides such as fragmentation--though that's far far less important on SSDs than HDDs. Apple's fast file copy mechanism also uses COW. I would suggest that it's an instance of listening to what your customers say rather than providing them what they need. They say file copies are too slow, but what they really want is a way to track versions, retain old ones, etc. It would be cool if Apple built on their existing approach with regard to file versioning.
