I guess the first thing to talk about is something others have probably already stated -- that learning back-end will give you a more comprehensive understanding of development. Yes and yes. So much goes into web applications that the front-end class only covers briefly (in comparison) but that we will cover in detail -- databases,2 integrating with external APIs, client-server interaction, things like Amazon Web Services,3 etc. You'll have an extremely solid understanding of how to architect software and how to think about the relationships between data, which will be invaluable for you as you begin to design (referring to designing how it works, not how it looks) and build your own applications from scratch.
Also, specifically for those interested in being a tech entrepreneur, Rails is fantastic framework to start with because of the ridiculously rapid and scalable prototyping it allows you to do. After this course you'll be able to spin up an MVP for your company in a matter of days.5 The importance of this from a start-up's perspective is huge. Most of the time and money that goes into app development isn't making the end-product that the user or client will experience, it's making all the versions that they will never see. You may think you know what you want your app to be, but you won't truly know until you've tried a bunch of things you learn that you don't want or that don't work. That fact that you, as your start-up's CTO or lead dev, will be able to rapidly iterate through this long, painful learning process on a familiar, scalable, flexible framework, will save your start-up oodles of dough and frustration. You won't have to contract more and more hours out to backend developers to figure all this out along with you, or to change features constantly as you see what works and what doesn't. You will be able to do it all yourself, and then have a solid blueprint of logic to pass along to front-enders (or do the front-end yourself) to make purty, or to mobile devs to re-package into an iPhone app.