Well I can't say in terms of cost effectiveness. I have had occasional posts that brought in good quantities of Steem which I accumulate so I thought I would try employing a little of it. Seems like paying to promote a post has the potential to cause the post not to disappear so quickly. Could be a good way to reach new people. I am definitely interested in learning more about post promotion and use of accumulated Steem (in its various forms) as advertising.
Having this post in the "promoted" section has definitely boosted its reads and likes.