Google Page Insights is a required tool to have when analyzing the speed and usability of your site. As you may know these metrics influence how google ranks your page in search results. If you frequently make changes to your web site designs than it becomes mandatory to check the metrics after each change to make sure that the design changes has not affected the score in any negative way. If you have many pages to test than manual testing can quickly become cumbersome.
Thankfully there are libraries that you can use to automate this process. Once such is given in this post which allows you to get Google Page Insight metrics using PHP.