The blanket statement, of you can just reinstall for a fresh build is not a valid one.
The effort regarding the 'clean install' does not work as advertised for all computers.
I have a fee machines I used in in the Insider Program. 2 Lenovo X series laptops and 1 Sony Specifically the Sony Vaio P.
The Lenovo's, were Win8 Pro machines, the Sony was WIn7 Ultimate (originally and Win 7 Home OEM provide build).
All were enrolled and running early thru the 10240 Insider Builds.
I tried this so called 'clean install' on the Sony and it failed to fully complete the first time.
On the second attempt, the install did complete, but it prompted for a 'Product Key' about 3 times. When it did complete, all the apps in the 'Start Menu' were note there.
On the third attempt it did compete, but it prompted me for a 'Product key' about 3 times, and I continued to sect skip. All the apps were there, but what I got was Win 10 home, not Win 10 Pro as expected.
So, this 'clean install', is not as advertised and your mileage may vary.
I tried this install multiple times, multiple ways (W7Pro, W8.1Pro, Upgrade in place, the new build using the available 10240 Insider ISO, the public ISO and an MSDN ISO), all with the same result. It would revert back to an unlicensed/activated Win 10 Home install.
My take away is that on certain OEM builds or maybe some OEM builds on these older machines, the Win 10 key cannot be written to the hardware as discussed. Seemingly you can only get Win 10 pro, on some of these older systems as an upgrade in place only or Refresh with wipe all. You cannot boot form a USB/ISO key and fresh build.
Again this was just my experience with this on this Sony Vaio P.
I have not yet tested the Lenovo's mentioned to see what happens with those OEM builds.