ROI is, of course, the ultimate goal of any advertising effort, so one might naturally ask, “Why would I ever choose an objective that’s not conversion optimized?”, or even “Why would I choose to optimize towards anything but purchase conversions?” It turns out the latter is the more complicated question, but one you can answer when armed with the right information.
It all has to do with how Facebook’s ad bidding works, which involves a combination of factors: your advertiser bid, estimated action rates (i.e. how your target audience responds to the ad), and overall ad quality. As Facebook notes, “together, estimated action rates and ad quality measure ad relevance. In fact, we subsidize relevant ads in auctions, so more relevant ads often cost less and see more results.”