O Boot Camp, which recently gained support for Windows 10, brings an unexpected new feature to OS X El Capitan 10.11.
According to the Twocanoes Blog, before installing Windows on Mac, it was always necessary to have a USB stick to copy the data from the operating system's ISO file and then install it on a second partition.
From the El Cap, at least in the latest Mac models, the entire process is done locally on the machine by creating a temporary partition called “OSXRESERVED” all in a transparent way for the user.
Welcome change and that should certainly speed up the process.
(via The Loop)