There are tons of tutorials about menus in general and drop down menus in particular, so why make a new one? Well recently i was surfing some forums and saw that a lot of people ask about that issue. i think this is a good enough reason:)
Zen coding is a sort of a shortcut library for writing html and css, so when you write your code it is faster and more efficient. In addition it help with writing errors like closing tags and so on.
