Yes these are purchased through some bots that people built to auto-vote posts. Some whales (big time power users on Steemit) also allow payment for x% of posts. For small minnows like you and I our votes are .01 maybe. For users with 10,000 in SteemPower their % votes could be worth $5.00 or more by itself. If you want to learn more about auto-voters or other bots, google Steem Bot Tracker and you'll find the page that has all the bots & whales listed. Is it worth it? I don't know if you get all your ROI in SBD, you do get more Steem though. Good luck to you.