This is a matter of retaining access and compatibility with much already owned software. A person receives no additional benefit to it beyond that - and that is a benefit that should stay with them.
Using a license to install Windows 7, 8, and presumably 10 on a PC associates that license with the particular PC it's installed upon, and trying to install an OS with that license on another key doesn't work because the servers at MS show that the license is already registered on a PC. If a person calls MS support, they can de-register the license from the PC its on so that it can be used on a new PC.
But in the case of a dual boot, the PC its registered with for one OS is the same PC to use used with the other desired OS.
And when it's a case of dual-booting on one PC, only one OS is used at any one time, so the license is never over-lapping its use - it is always used as only one single license running just one OS at a time.
I'm not sure how it's gonna work, but I do intend to keep my multi-boot systems...
Vladimir, we are not sure if that is allowed or not. I can tell you this it is a pain to do. It requires using partitioning, image backup, grub rescue boot cd, windows 7 repair cd. Cloning doesn't work that will fail.
Simple, upgrade 7/8.1 on one disk and dual boot with 10 in insider test mode on another, it will keep getting new updates before they arrive on full W10.
MS promises to keep insider version for some time to come as free Windows so nothing stops us for using it on another computer.
What's a pain to do? Dual booting?
On as single disk in a laptop with UEFI, I would label it as pretty complicated at least.
I'll have a go later. My dual boot on my desktop with separate SSDs for each OS was plain sailing.
It's only a pain if you are dual booting 7/8 and Win 10 insider Preview either on the same or separate drive. Win 10 messes up the boot manager every upgrade. I do run multi-OS but I don't set it up for dual/triple boot. I just select a boot drive on startup. However, it's not really very difficult to fix a boot problem. It's just a waste of time doing it over and over again.
I might have read your response incorrectly but I have dual boot win 7 and win 8 with a win 10 insider preview with no issues whatsoever. Beyond easy. That being said I have only done it with separate SSD drives. When I do a insider preview install I always disconnect the other drives. I can see where it might be a problem trying on the same drive with different partitions.
What I meant was, it's ok to dual boot 7 & 8. But if you add Win 10 preview in the equation and with all those build upgrades, it can mess up the boot setup.
Just like you, I install Win 10 on a separate SSD and pullout the other drives when I do an upgrade or clean install of it to avoid those dual boot mess.