heroku/12factor — pull request #9 by stevecrozz (2014-03-03 18:14:00+00:00)
Title: Correct claims about how Jammit works

While Jammit can use the filesystem as a build cache at runtime (much
like the asset pipeline), the official recommendation from the Jammit
documentation is to build the assets at build-time. In fact, that's
exactly what the 'jammit' command is for.

http://documentcloud.github.io/jammit/#precaching