Benefits of mapping the customer journey?

Has anyone successfully introduced the concept of a customer journey when everyone else at the company was unfamiliar? How do you describe the tangible benefits to the business? Which functions are involved in the mapping exercises?

I've personally seen life without a customer journey...I know it's messy. I work in early startups, where the mindset is often, "do whatever it takes to make each customer successful" and so there's not a well-defined path to success. How can I start to socialize the concept to get buy-in?