One of my favourite episodes of the Simpsons is where Homer discovers he has a long-lost brother called Herb. Of course Herb is the complete antithesis of Homer. He is successful, slim with a full head of hair. He runs a successful car (or automobile in the native American) manufacturing company called Powell Motors in Detroit. Herb is overjoyed to learn of his brother and they start to spend a lot of time together.
After a while, Herb realises that Homer is the epitomical average American guy and therefore the best person to design a car for ordinary Americans, so he lets Homer loose and gives him free rein to design the next car from Powell Automobiles. Of course, being the Simpsons, it is an unmitigated disaster. The car that Homer designs appeals to absolutely no-one and Powell Automobiles ends up going bust.
So where did Homer go wrong. Quite simple really – he did not focus on who his customer were or what they might want. He simply kept adding features until he could think of nothing else to add. What this did was inflated the cost (because there were so many features) and reduced the appeal, because who wants something that is average at everything.
A really simple idea, a use case is almost a story that defines what the user will end up doing with the product. The benefit in doing this is that everyone can visualise exactly what the product will do. The use cases “As a racing driver I want to get around a lap in the quickest time possible” will yield a very different product to “As a commuter I want to complete long journeys comfortably without using too much fuel”.
The benefits don’t end with development of the product either. If we have the use cases, testers can immediately understand the natural paths through the system and can make sure their tests fully cover these paths (as well as looking for where the users might stray off the path. Because use cases are written in plain English, Sales & Marketing can immediately understand what the product is about and gear up their materials accordingly.
So if you want to end up with a Bugatti Veyron (and not a Homer special) – it’s a very good idea to think about who’s going to use your product.