The complexity of our front end code keeps increase year over year. The tools are changing and it feels like you need to know more and more stuff just to be able to use a new framework or boilerplate and idea. Codepen has been an essential tool in my learning and coding small pieces of a project. It is just both easier and faster to get an idea out there. The feature set is always increase and the sharing of your pens makes collaboration something that is dead simple.