Et voilà, the desktop
If you install the Update over a copy of Windows 8.1 that hasn’t been modified, on a machine that doesn’t have a touchscreen, mirabile dictu, Windows boots directly to the desktop, by default. Presumably, new computers without touchscreens and clean installs on computers without touch screens will exhibit the same refreshing change.
Experienced Windows 8.1 users know that switching to boot-to-desktop involves a simple two-click setting. But folks who don’t know -- or don’t want to take the time to learn -- will suddenly find themselves in a familiar environment, not at the mercy of the Metro tiles.
To me this trivial change is by far the most important change in the Update.