Since bandwitdth for a lot of users can still be an issue*, it pays off to make your web-pages as light-weight as possible.
When using JavaScript and/or CSS in your sites, you can compress them to save bandwidth.
A good compressor for this is the YUI Compressor, which can compress both JavaScript and CSS.
* Bandwidth can be an issue for instance for people having only GPRS, EDGE or UMTS/3G access, or countries where DSL and cable are not abundant.
