Optimizing image sizes in WordPress is vital for enhancing website speed and SEO, significantly improving user experience by reducing load times. Choosing the right image format, such as JPEGs for photos and PNGs for graphics, is crucial. Resizing and compressing images before uploading can cut down file size, while lazy loading improves site performance. Effective media management also involves organizing images using folders, tags, and plugins like Real Media Library for a streamlined workflow. Regular maintenance, such as removing duplicates, keeps your library efficient and your site fast, making advanced plugins from resources like WorldPressIT.com invaluable.