Actions that run when you sign in
Until now, anything the platform wanted to change for people who already had an account had to be done by a database migration, which meant it could not be done at all without shipping a new version. Administrators can now declare an action that runs for each person the next time they sign in — either once, ever, or on every sign-in — and use it to bring existing accounts in line with new ones. A typical use is refreshing what is pinned to everyone's home page.
Anything an action changes belongs to you afterwards. A once-only action never runs a second time, so if you re-arrange your pinned items later, they stay exactly as you left them.
The first thing riding on this: the icons on your Apps grid. Apps that were showing the generic puzzle-piece placeholder now pick up their real icon, so you can recognise an app before reading its label — including apps you install from the Store later on.