When you own a online store or a large website you know you need to keep your images small in KB’s.

Source; Google
https://developers.google.com/speed/docs/insights/OptimizeImages
Optimize Images

Contents
Overview
Recommendations
Optimizations for all types of images
Optimizations for GIF, PNG, and JPEG images
This rule triggers when PageSpeed Insights detects that the images on the page can be optimized to reduce their filesize without significantly impacting their visual quality.

Overview

Images often account for most of the downloaded bytes on a page. As a result, optimizing images can often yield some of the largest byte savings and performance improvements: the fewer bytes the browser has to download, the less competition there is for the client’s bandwidth and the faster the browser can download and render content on the screen.”