1. What does it mean to precompile files? What does this have to do with Coffeescript and Sass files? Does it only have to do with Coffeescript and Sass files?
Precompiling asset files is a way to help browsers make fewer requests to your webserver to display items on your page. Precompiling is done in Rails via the asset pipeline.
Precompiling consists of 3 tasks: concatenating assets, minifying assets, and providing a way to access those assets in other languages.