The new portables can be fitted with 12.5 mm disks

Even if the vast majority of the 2,5" hard drives are 9,5 mm thick, there are models that are 12,5 mm thick. These are primarily disks of large capacity that, from time to time, certain manufacturers produce in order to offer a disk larger than the competitors.
It was impossible to install them in the majority of the Apple portables, however now it will be possible in the MacBook and MacBook Pro unibodies. The only real interest is that it will no longer be necessary to raise the question about the thickness of a disk before buying it to install in one of these machines.
On the other hand, the Superdrive remains at 9,5 mm and this limits the options of change in the case where, one day, you would like to fit a compatible Blu-ray drive.