Basically, choose lossy if you prefer a more optimized image weight (faster image). There are 2 main types of compression levels available, Lossy and Lossless. A faster site is a more search engine friendly website (SEO friendly). They will find the information elsewhere or give up all together. This causes lag and if your page takes way too much time to view on their cell phone, tablet or desktop, your visitors won’t want to wait around for your page to load. The browser and/or server will take too long to respond because there is too much information to read and download. If you don’t optimize, your images will weigh down on the web page that you are trying to serve to your visitors. And when left untouched and raw, they contain a lot of heavy information that is not needed to be served on a website. Most digital cameras take very large high quality photos. There are several reasons you will need to optimize your images for web.