Facebook shares are for promoting an individual Facebook status / photo / video. A Facebook user will share your status on their own wall to all of their own friends for the maximum amount of exposure and traffic. Facebook shares are arguably more valuable than status likes for this reason.
If you're trying to promote an important status, such as a contest, event, promotion, announcement, or something of major significance, Facebook shares will put many more eyes on your status and will help increase it's visibility in the Facebook newsfeeds so more of your fans will see it as well.
It depends on how much exposure you want for your status. If you want to drive as much traffic and attention as possible, a large order will show a noticeable difference. Buying status likes along with Facebook shares will make a noticeable difference and will look more organic; most of our customers buy both Facebook shares and Facebook status likes together.