The asset pipeline is great and confusing at the same time. It performs differently in development than it does in production, and as such you can’t be really sure everything is going to work once you deploy it, unless you really understand it, of course.
OK, before you go yell at me, I know enabling detailed error messages on a production web application is a Bad Thing™. The security guy in me hates finding a production application that spews back all kinds of details to a user when something goes wrong, and I’ve had many a developer disable detailed error messages on their production applications.
Cookies are used to store a variety of shared state information between your browser and a web server. The most common use for cookies is to maintain your session state, since HTTP in itself is a stateless protocol.