When you developing a template for a new site you often get stacked, and hit your head against the wall: the code outputted by Joomla sometime severely limits your ability to format the output as you wish. This is true not only for Joomla 1.0.*, but partially for the Joomla 1.5.*. Yes, partially, because you can do things here - and you can do a lot. Searching for a solution for a problem I had run into developing a template for one of my clients I found this great tip of Jonathan on his blog on http://www.beckettwebdesign.com:
Template is an essential part of a Joomla site. It's not only simple HTML/CSS/PHP/JS wich let's you show your content, it's a genuine shell with endless of possibilities for success - and failure. There are defined not only how your site will look like for your human visitors, but also for searchengines too. So it's your primary tool in your SEO efforts.
And also it's first line of your defence too. Lots of security holes can be opened with a badly written template! And also, don't forget, that might be the biggest resource hog - so the first place to optimize your site's performance.
More: has a tremendous amount of power built in. You should unleash that, and master it.