This works well assuming you're disciplined about it. When I graduated, I knew I wanted to start my own startup, but I planned on bootstrapping and needed money. I worked two years exactly, living cheaply and saving as much as I could.
My job was comfortable and I really loved it. It would have been very easy to stay. The advice to start "now" is really a reminder that if your answer is always "tomorrow," you'll never get started.
I'm not sure discipline has any place here at all. If there aren't 10 moments every day in your corporate job when you wish you were in a startup and could do things your way, then you probably wouldn't enjoy being in a startup anyway.
My job was comfortable and I really loved it. It would have been very easy to stay. The advice to start "now" is really a reminder that if your answer is always "tomorrow," you'll never get started.