Smarty has it's place - in a work environment of a team of 12.
But if you are the ONLY one working with it then it is a waste of time a resources to load that whole lib. I built my own templating system that is WAY faster than smarty while still allowing PHP code inside of templates. The reason it works for me is because only 1-3 people will be working with it and they aren't going to be doing stupid stuff with PHP code.
An example is wordpress. It is a blog for 1+ people so they don't mess with something so big as smarty. If the author wants' to hack his own site from the template files - they won't stop him.
So what is your need? Group? or Personal?
Smarty >= 10 > ob_start() and PHP