主要是优化图片大小的，有 smusher 这个 Gem

https://github.com/grosser/smusher

$ smusher /apps/ts/public/images
smushing /apps/rs/public/images/social/facebook_icon.png
2887 -> 132                              = 4%

smushing /apps/rs/public/images/social/myspace_icon.png
3136 -> 282                              = 8%

smushing /apps/rs/public/images/dvd/dvd_1.png
5045 -> 4                                = 0%
reverted!
...

原文： http://adventuresincoding.com/2011/11/speed-up-your-websites-with-smusher