This is a great way to increase your website’s performance without any drawbacks to this method. Not that there are great drawbacks to methods like using gzip on your files, but gzip does create some extra CPU load on your server. The method here will reduce file size (thus decreasing your webpage load time) without any drawbacks.
Yahoo has a web-based tool called Smush.it which does a lossless optimization on images to reduce their size. The tool strips unneeded metadata, repeating pixels, and chunks from images. The image quality is not reduced, but the filesize is. It’s extremely easy to optimize and reupload your optimized images – and there’s no reason not to do it for the average website. Your site will load faster, you’ll keep more users with slow connections on your site, and you might even save some bandwidth on your server.
You can use Photoshop to further decrease the size of your images, but then you’ll have to decide between image quality and size. Yahoo’s Smush.it doesn’t sacrifice image quality to reduce the size.