There are dozens of metrics that savvy marketers review to asses the success of their campaigns. And, “savvier” (cough*manipulative*cough) marketers may highlight metrics that are improving and downplay ones that are not, making it tricky to decipher if a campaign is doing well or not.
If you are only going to review one marketing metric, the most telling one is conversions.
Now, conversions may be different for each campaign. You may want to convert people to download your white paper, or subscribe to your blog, or use a referral coupon code, or make a gift, or purchase a product from your store.
Ultimately, each of your marketing campaigns should have one conversion goal. One action you want the audience to take. If you notice that conversions are down (or up!), the other metrics can give insight into what didn’t work (or what did!). The myriad of metrics are helpful to fine-tune and assess your campaigns, but conversions are the ultimate KPI to watch to make sure your marketing is delighting your audiences and raising your bottom line.