I think you want to check out
The decision of when to use SSI, and when 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.
"Just because you have not felt the need for it does not mean that it is not desirable..."
Oh most certainly not :) If the case was wheter I felt a need for something to allow something's existence, the world'd be pretty boring :)