Larger image file sizes will increase download time. Some users will be paying per KB of mobile data that they download.
We would also need to consider that there may be multiple images used on a page. Few users are happy to wait on the web, and large images can be particularly frustrating for users with low bandwidth.
Users do not tend to wait for images to download before assessing their options and following a link. If images are slow to download, users may miss the complete message.
As huge image files can drag the page-load time of your site down and directly affect your rankings on search engines, so be sure to resize them before you upload.
SEO, Usability (Large images will slow page download. This reduces user satisfaction, especially on mobile devices.)
This checkpoint will scan the image for the image size to see if it between 50 - 200KB, if the image file size is larger than the specified range then it will be reported as an error. Note that there are other variations of this checkpoint that specifies a different file sizes. The checkpoint will flag images based on the file size specified in the checkpoint.