As Lewis Carroll (and later, George Harrison) so famously stated, “If you don’t know where you’re going, any road will take you there.” If you’re running a campaign on social media without taking the time to use an analytics tool to assess if you’re getting the results you want to achieve, then you really don’t know where you’re going.
Social media KPIs matters because it tells you where you are, where you want to go and where you should be heading if you want your social media marketing campaign to work. Otherwise, you're driving towards an unknown destination, with no map to guide you and time being wasted.