Matthew Setter as a post on his site that suggests that microframeworks make for lean applications, such as one he recent built using the Slim framework.

Recently I built a new application using SlimPHP, a PHP microframework, instead of a full-stack framework, such as Symfony or Zend Framework 2. In this post, I start discussing how taking this approach has lead to a leaner application design. [...] Before I get too far along, I want to make one thing clear, I'm not bagging full-stack frameworks. [...] Technically, you don't need to bring in more than you need. However, often times, these frameworks still do have a lot of overhead which you may, typically, never need. [...] Whereas microframeworks, assuming they follow The MicroPHP Manifesto, especially SlimPHP, give you the minimum you need to start building a web application.

He goes on to talk about why he made the choice of Slim for his application and describes a bit about what the application does. He talks about some of his main needs when creating the site and how Slim matched up with most of them (with a little help from a few other packages). He included other libraries for YAML parsing, Markdown output formatting, caching and others to round out the application but Slim was at the heart of it. He ends the post by pointing out that taking this lightweight approach was a perfect fit for his project and that, while there were other choices, Slim fit his needs best.