Sites and apps are including more and more high-quality images. The more you can compress images to reduce their size in bytes, the smaller your bandwidth, the faster your site will load and the happier your users will be. But when compressing images, you need to make sure you maintain high visual quality.
Most web sites and mobile apps use the popular JPEG format to display their images and user uploaded photos. The JPEG format has efficient built-in compression that reduces image size while maintaining a reasonable visual quality. But you can reach much better results using more modern image file formats.