Use the term Template Engine in a PHP forum and the word "Smarty" will inevitably crop up. I like Smarty but, similar to a few PHP libraries, it's very bloated.
I try to keep my applications lean and mean - small, fast, and adaptable. Unfortunately, Smarty disagrees with my needs. It's bloated design while packing a mighty punch, uses a chunk of memory and processor time I dislike. Since I also develop open source apps which end up on shared hosts, my concerns are even more justified.
He talks about what Template Lite is and what kinds of advantages it has over Smarty, including staying try to its name. Pádraic measures it as not only being faster but also having 50% of the memoery footprint that Smarty does. He seems to favor it for those places when he just needs something light and easy on a site.