When I am trying out/learning a new library or framework, I do a lot of tinkering, looking around and reading the source code. Coffeescript output is definitely readable, but you need to take a tiny bit of time to translate the coffeescript output, to the actual source so you can read it, checkout the comments etc to understand how you are supposed to do something. This added bit of time adds up quickly for me.

For example when I was first learning backbone, which is only around 1000 lines and very well documented. I was constantly reading the source code to understand why something wasn't working for me or how to implement something. Projects typically aren't nearly as well documented as backbone, making understanding the sourcecode even more essential.