Google Analytics can help you learn more about the behavior of your client’s customers because it shows you how:
they perceive her products
likely they are to become a regular customer
they interact with her website
likely they are to click her ads
Linking a Google Analytics property to your AdWords account can help you to analyse customer activity on your website after an ad click or impression. This information can shed light on how much of your website traffic or business comes from AdWords, and help you to improve your ads and website.
Google Analytics has a powerful segmentation engine. Instead of looking at your audience in large bunches, you can break it down into its component parts and understand how each part interacts with your site—then bid, message and direct traffic accordingly.
Read more here: https://support.google.com/adwords/answer/6168606?hl=en