i just bought a new 2015 MBP 13" and it came with Yosemite which I used for a few days. I attempted to perform a clean install of El Cap from a USB stick. I booted from the USB, erased the Macintosh HD and renamed it the same, then installed El Cap from the USB. However, when it booted up, it asked me for my iCloud credentials. I entered it in, and then it said everything was setup. All my trackpad settings and wifi network from Yosemite automatically appeared in this supposedly fresh El Cap install. How did these settings show up in my clean install? I would have expected to have had to re-enter everything just as I had when I first used the MBP.