When you capture in RAW, no image compression is applied, so you are retaining the highest image quality possible. With JPEG, which is the most common alternative to RAW, image compression is always applied to reduce the file size, even when the highest quality option is selected. As a result, there is a risk of artifacts (random pixel variations) in the image. Also, because JPEG compression divides the image into blocks of pixels, in some cases a grid pattern may be visible within the image. Capturing in RAW completely eliminates the risk of such artifacts. The price is a larger file size, but the benefits can be significant in some cases in terms of image quality.