[SODaniel]

Cross account deduplication has nothing to do with making improvement client side, it's all about keeping storage costs down for the provider.

The only type of deduplication that matters to consumers is account specific deduplication, and that saves no data for the provider unless you charge for non deduplicated storage.

[humbledrone]

Cross-account deduplication does have a client-side benefit: duplicate files don't need to be uploaded. E.g. your 300 GB iTunes library might sync to the server in a couple of minutes, rather than days.