yes, only a marketing function. It is, of course, awesome when they are profitable, like two days ago when they all were giving out 2X-3X due to the dip in the market and some panic. But essentially they are only tools of marketing, for whatever reason you may have.

You could also add sponsors, ads etc to your blog before you trend it, that way you can get "coca cola or Pepsi" to pay for your marketing in exchange for them to be seen on a trending post... There are many ways to monetize what you do, just be creative.