Promote is entirely useless from the point of view of the vast majority of users. I believe I used it once or twice .. this 'burning' of currency having a benefit to the health of the overall econ is entirely lost on most people, if indeed it is still the case!

People do not want to "understand" such things .. who the hell has time for it,and even if they did understand the only reason they will sacrifice STEEM, or SBD .. is if it has a 'real' and noticeable benefit.

A far better idea, in regads to "promotion" is to allow users to add their own STEEM to the associated rewards of their, or any specific post. This adds to the curation rewards to those who have participated - upvoting and commenting .. and it also serves to promote the post, making it more visible, more interesting to potential readers, and perhaps even puts it on the trending page.

This would be a great way to promote or support a project, and has the added benefit of taking pressure off of the rewards pool!