For my ads getting sales on my courses, I completely optimize by Return On Ad Spend because I do not care then about likes either. I want sales and if it is not sales forget it!
For Steem, we have a huge community already and branding is one of the top goals at this point because branding alone can lead to a price increase as well as a user increase. While I would prefer to track sign ups directly, with Steem we can think more like the top brands in the world and just go purely for brand recognition without having to demand an immediate return on the ad spend as we do selling our own products and those for clients!