The site sends fake traffic to your website, just to increase its own google page rank.
sharebutton.to referrer spam is designed to create repeated site requests to the website it lands on. The benefits that referral spammers have with this tactic is that it will help them advertise the website they want people to visit and it will also improve the spammers search engine ranking.
Solution: Add a filter in google analytics to remove the traffic from your reports. https://support.google.com/analytics/answer/1034842?hl=en