Too Long; Didn't Read
Responsibility is when your site changes the design based on the user's screen he/she uses if the visitor is coming to your site using a personal computer - your site looks one way if smartphone - another way. If you want to make money with your site then responsive design is crucial to have it. People now days have such a short span for waiting and clicking and searching that if you make them think of what/where/why then that's it, withing few first seconds you just lost a customer.