The Touch Bar in Mail does a lot more than offer you QuickType suggestions. It actually surfaces potential contact suggestions based on your email history, as soon as you click on the address or the CC field.
While going through your email, the Touch Bar lets you quickly compose a new message, flag or reply to an email, and even predicts whether you might want to move an email to a certain folder, based again on your history.
And while composing an email, you can highlight certain text and the Touch Bar will then surface formatting options, so you can change the font and color or make your text bold or italicized.