Proxy caching can confuse or defeat both of these objectives. Caching is a simple concept that can occur at several levels, for example in your browser. When a Web page is requested, it is saved to disk. If it is required again, the disk copy is used instead of fetching the page again over the internet. This technique is used in all modern browsers such as Netscape Navigator and Internet Explorer.
Most people probably leave it at the browser default setting.
However, you may be being served cached pages by a middleman as well. It then provides cached copies itself instead of getting them direct from the source. The local proxy server gets the page for the first user requesting it, saves it on disk and forwards it to the user. Subsequent requests from other users of the ISP's cache get the saved copy, which is much faster and does not consume Internet bandwidth. This saves the ISP a lot of money.