Think about the sites you visit on a regular basis. Facebook, StackOverflow, Twitter, Reddit, Youtube, Github, Khan Academy… just name any big site you spend time at. What do they all share in common? They prompt users to create an account and participate in creating and sharing content. That is the modern web. WordPress is the old paradigm, a one-way channel from site owner to visitors. Like watching TV.
BuddyPress opens it up so that your visitors become contributors, which can grow your site content exponentially. There is endless business potential here. Some use case scenarios: collaborative education (like Udemy), social blogging (like Medium), social portfolios (like Behance), social commerce (like Etsy), etc. Business models include paid subscriptions, tiered member levels, and more creative forms of advertising (because your visitors log in and you know them).