[EdSchouten]

In my case I observed a ~2% reduction in data storage when attempting to store and deduplicate various versions of the Linux kernel source tree (see link above). But that also includes the space needed to store the original version.

If we take that out of the equation and only measure the size of the additional chunks being transferred, it's a reduction of about 3.4%. So it's not an order of magnitude difference, but not bad for a relatively small change.