Most marketers are overthinking things when it comes to Facebook (or any traffic source) and which conversion metrics to look at. On Facebook there are dozens of different data points you could look at to decide whether to kill and ad or to keep it running. The only metric that matters to me when I am optimizing a campaign is the CPA. If you are doing lead generation this could mean your cost per lead. If your selling products than the CPA you should focus on is the sales revenue.
One of the biggest mistakes that new marketers make when launching ads is paying too much attention to their cost per click. While this metric is important, you shouldn’t be making decisions based on it. For example, click bait ads will usually get a lower CPC but not convert as well after the click. A more detailed ad might get more expensive clicks, but a much more qualified user that ends up being worth more.
Especially if you are a new marketer it can be very overwhelming to try to analyze a ton of different data points to decide on an ad. So my advice is to keep it as simple as you can. Is the ad making money? Keep it. If not, pause.
Keep testing my friends.