There are two reasons to articulate your use case. First, it helps your staff, your designers, your marketers and your sales force get on the same page about what they’re building and growing. And second, it might be unrealistic. You might be hoping for a market that’s far bigger than it is, or to solve a problem that’s too easy (or too difficult).
From “Articulating your use case (what’s it for?)” by Seth Godin