On most WordPress sites, images make up the majority of page weight. One uncompressed hero photo can be larger than your theme, plugins and fonts combined. Fixing images is usually the fastest way to improve Largest Contentful Paint (LCP), the Core Web Vitals metric most sites fail.
An image optimization plugin does three jobs automatically: compress images on upload, convert them to modern formats like WebP or AVIF, and bulk-process the images you already have. The differences are in quality, limits and how you pay. I have compared 9 Best WordPress image Optimization Plugins. Compression quality, WebP and AVIF support, free limits and real pricing for WordPress sites.