Niko Kitsakis on creating well design dialogs:
The text change reflects the fact that you could now have multiple applications open at once. Otherwise it’s not important to our example so let’s focus on the other elements. Two trends are going to become apparent, speed and safety:
The icon with its exclamation mark gives you an immediate idea of the character of the message. “Be cautious” it says, “pay attention.”
Then we have the buttons which no longer say things like “Yes” or “No” but have been changed to verbs which say “Save” and “Don’t Save”. If you glance at those verbs you don’t have to read and understand the text to know what’s going on.
Now look at the new layout of the buttons: Of those three, the first button – Don’t Save – will make you lose data while the other two – Save and Cancel – will save data. In this new layout, the button that will make you lose data stands separated on the left from the two buttons that won’t. This reduces the chance you will accidentally press the wrong option.
Lastly, the most commonly used option – Save – is highlighted and can be activated by pressing the return key on the keyboard.