Yes, it is supposedly for Insider Builds going forward, but...
I suspect if it is well recieved and proves beneficial, it will be employed across the board, like for the Fall Creators Update to everyone, when it becomes publicly available.
Personally I was not impressed when they did the UUP (
Univeral
Update
Platform) thing as I didn't see any noticeable improvements to my experience, if anything it seemed to have lengthened the time to install a build.
As I said above...... We'll see.
Ideally, as I understand it, it is suppose to give the user more time at the front end of the process to use their computers normally and is suppose to shorten the time at the end of the process (after you click the restart button).
As this (the download and first stage of installation) is already suppose to happen in the background and the "restart" is suppose to happen only during "Quiet hours" I'm not sure that many will actually notice any changes or their associated impact, except those of us who actively and manually pursue such things.