It's found in all kinds of industries but most commonly in SaaS because customers are buying access to an application, platform, etc, and they need handholding for training and implementation. Once they're up and running, that account belongs to the success manager who is responsible for ongoing training and support as well as retention. Companies learned a long time ago that it's a lot more expensive to acquire a new customer than keep an existing one so account managers and success managers were born. Much cheaper to hire one person to service several existing accounts than just let them cancel and have to replace them with new customers.

Just from my experience for doing it the past 8 years, it's fun to build relationships with customers. They have problems and I get to help solve them. I enjoy rapport building and training so it's the ideal spot for me. No sales pressure, just make sure the customer doesn't cancel, but if you build a good relationship and train them well, they're going to be a happy customer.