Especially if you happen to be quoting someone, it adds a touch of class to use these rather than their boring unicode counterparts. This site outlines the differences between the two, and for convenience I'm posting each here so that either one can be easily copied and pasted:
Left quotation mark. Hold down ALT and hit 0147 on your numeric keypad.
Right quotation mark. Hold down ALT and hit 0148 on your numeric keypad.
Below is as an animated GIF showing each of the left and right double quotation marks as well as the plain old unicode ones in CharMap, and keystrokes you can use to type the former if you're so inclined:
|A handy animated GIF outlining them all.|