There are a couple reasons to do this:
1) No one wants to be the first person to share something so you need to "seed" your posts with a certain number of "shares" to get the ball rolling. See: Bandwagon Effect
2) Perception is everything online. The last thing you want on your site is a bunch of social media icons all over the place with a bunch of zero's on them, it looks bad.
Plus the number of shares adds credibility to your site and makes it look more popular. As a result, people will take you and your content more seriously.
People want to go where the action is, it's similar to "peer pressure" in a way. If your site looks like it's unpopular, then that's not a place people want to go or share with their friends.
Of course the byproduct of all this is gaining a larger following and making more money.
It's easy to get frustrated when you're creating posts that have true value yet it seems that no one is paying attention to your site.
This is a great way to jump start things...
But if you don't want to go all out with "fake" shares, there's an option within the plugin you can use that will still give you a desirable effect that won't hurt the perception of your site.
You can download it here: https://www.dropbox.com/s/7l9pgch8d9...share.zip?dl=0