Here’s a quick example of why image optimization for your website is so important for speed and mobile-friendliness.
The image in the design of a small thumbnail only needs 300×200 px to cover, but the developer placed an image of 1600×600 px, so it’s like loading a full-sized poster when you only need a tiny thumbnail. This is in reference to these images:
Now check this out, as an example, I’m using the Commercial Roofing image to optimize from 218kb on that image to 59kb. Using the ImageOptim tool for Mac.
Now that is a lot, especially when it’s multiple images on the page like in our case, you can save megabytes of data that a user has to load.
Again, most web developers do good work, but it’s not always going to be pristine and/or adhere to the greatest web standards. The quality of work is apparent when it comes to loading the website.