The importance that lies within analyzing your ads is immense; as that analysis is compared against the ad’s goal and whether or not it reached it . This action of comparison is referred to as Key Performance Indicators or KPI for short. Without KPIs you won’t be able to understand your data or measure it per your goals, which could mean losing time and money without value or success, however with KPIs you can set a tangent to measure whether your ads are drifting away from their goals or staying true to them. Neil Patel elaborated in his article on different KPIs and which are reliable to measure against and which are useless. Let’s say you made an ad and it’s goal is to drive traffic to a blog post then your KPI is CTR (click through rate), however you define whether or not the percentage of CTR is successful by the actions taken from that traffic, i.e: 
  1. Did they sign up for your newsletter after reading the blog?
  2. Did they latter on purchase from you and what was that percentage of conversion? 
  3. Did the converting rate earning you enough money to sustain the ads or is the ad cost higher than the conversion rate?
All of these questions are related to your campaign’s success. Depending on the answers you can rate and improve as you go. So if your CTR is low; hence you aren’t getting enough traffic to the website, you could need to:
  1. Reconfigure the ad’s content or design.
  2. Consider the ad’s frequency maybe you have shown it to the same audience -in case of a small audience- a number of times so they grew unresponsive to it. 
  3. Readjust the ad’s target audience.
Bottom line is that defining you KPI depends on the ad’s goal and it doesn’t just stop there it’s related to further processes ones we intend to discuss further with you.