Microsoft Word's blog
Styles help keep the look of your document consistent, and save many keystrokes when multiple formatting options must be applied to a page element. If you use styles in your Microsoft Word documents, you are already saving yourself a lot of time, effort and keystrokes. But is it possible to be even more efficient when applying styles in a Microsoft Word document? You bet there is!
The easiest way to apply a style is to use the mouse to select from your list of styles in the toolbar menu. Easy: yes, efficient: no! Switching between keyboard and mouse will really slow down your typing efficiency.
How to Link a Style to a Keyboard Short Cut
You can apply styles and stay entirely on the keyboard by linking a one- or two-key sequence to a particular style.