Pretty much every embedded system used for a consumer electronics device is driven by a state-machine. They are really fairly fundamental to embedded development. I suspect this guy is talking about (and dealing with) mostly web developers and people who don't sit so close to the metal.
In my current position it's entirely expected and reasonable to write some code and then half way through go back and rip parts of it out and turn it into a statemachine. Though generally we produce fairly detailed designs of our SMs first.
The act of going back over previously written code that is headed down the wrong path to refactor it to be more flexible/modular before you write your next feature with that code is almost always worth it. It's not worth it if you're never going to extend this feature ever again, but chances are, if you're revisiting a feature right now you'll revisit it again later.
In my current position it's entirely expected and reasonable to write some code and then half way through go back and rip parts of it out and turn it into a statemachine. Though generally we produce fairly detailed designs of our SMs first.