If I actually used Windows 7 or 8 on my laptop, this is just the kind of nutty thing I might try. Bear in mind that Windows 10 is still effectively a beta product, so this is not for the faint of heart - but it's interesting that this might be available when the production version of Windows 10 is available as a free upgrade for current Windows 7 and 8 users. Most "normal" Windows users would be more comfortable upgrading in this manner than burning ISOs to DVD and so on.
GHacksThe only options you had previously to upgrade from an older copy of Windows to a new one was to run the installer either while the installed operating system was running or by booting from an installation disc or Flash drive to initiate it.
Microsoft wants to make things more comfortable and has added an option to upgrade to Windows 10 using Windows Update.
Windows Update is the operating system's updating service which is best known for delivering security patches once a month to supported Windows devices.
The core benefit of upgrading via Windows Update is convenience. You don't need to download the ISO image of Windows 10, don't need to burn it to DVD or copy it to a USB Flash Drive, and don't need to run it afterwards on your system.