Conversion is not even sufficient. Conversions tell you how many people went through your ad and successfully bought something, but the value of ads is *how man

Conversion is not even sufficient. Conversions tell you how many people went through your ad and successfully bought something, but the value of ads is *how many people who weren't already going to buy something bought something through the ad*. E.g. people might be seeing an ad for Target after typing "target" in Google. The number of conversions through that doesn't matter and should be discounted. People might be seeing an ad or hitting an affiliate link for a website they already use regularly, if they go there hours later it doesn't mean your ad is effective.