This probably indicates that we need to do a bit of work on our documentation :) You're right about the general purpose - however Shunter also handles front-end assets: images, CSS, and JavaScript, as well as making it easy to extend the rendering engine.

In terms of benefits of using Shunter over a home-rolled solution, the same question could/should be asked of any framework. Shunter is very well tested, has been used in production on a large site for a number of years, and is used to serve hundreds of thousands of requests. It will also be supported by a large development team for the foreseeable future.