Both mod_pagespeed and IISpeed gives you the following:
- Image optimization-images are resized before they are sent if the HTML displays them with a smaller size; their format is changed to send the most appropriate one without quality loss; and unnecessary headers (which can take up a lot of space) are eliminated.
- Conversion of image sets to Sprites to reduce the number of requests.
- Elimination of comments in HTML files.
- Cache optimization.
- Optimization testing via A/B tests.
Apache users can learn more about mod_pagespeed at:
IIS users can learn more about iisspeed and Web Optimization in the following urls: