If the "Save customize configuration on Exit" tick is enabled on the preferences window all the time, every time 3ds max is closed, it saves all windows positions.
Because I like to have the UI windows always in the same position, I have this option off, but from time to time I do some twiking on my UI and to save changes I have to do the following:
1. customize > preferences > turn on "Save customize configuration on Exit"
2. Exit 3ds max
3. customize > preferences > turn off "Save customize configuration on Exit"
Instead of this, it would save much time if there was a button on main screen with just a "Save UI"