WHATS SSI?
SSI (Server Side Includes) are directives that are placed within HTML pages, and evaluated on the server while the pages are being served. They let you add dynamically generated content to an existing HTML page without having to serve the entire page via a CGI program or other dynamic technology. The decision whether to use or not use SSI, and whether to have your page entirely generated by some program, is usually a matter of how much of the page is static, and how much needs to be recalculated every time the page is served. SSI is a great way to add small pieces of information, such as the current time. But if a majority of your page is being generated at the time that it is served, you need to look for some other solution.
