Product Sense & Dollars

Product Sense is that elusive ownership of product development whereby the dev team not only know what they're doing, they understand it, & they can articulate it. That's heady stuff. More than that, they can tell the story in their own words, not just parrot what the marketing or product person has defined as the 'only way' to represent the product or the company.
Stories are important for agile, mostly because things can change, so the story has to change little by little - not be replaced by a new story. There are interpretations, like any good folk tale, nuances, expressions, that all come together to make a long-lasting piece of culture that is acceptable to all levels of society, if you don't mind my metaphor running away a little there. What marketing sells must reflect what product intended & what the devs are creating. The only way that can happen is if everyone understands the story & can retell it without having to use a dictionary to determine the meaning of a specific word out of context. The story should not be in French if the audience only speaks English. Admittedly, you sometimes have to use bad English as the lowest common denominator, but you have to use a language that everyone gets.

If the team - & now we can talk about the wider team that includes the non-technical - speaks one language, then they can tell that story to others not involved in writing the story. They can all evangelise, they can share in enhancing the story & making it better. This sounds a little Celtic, but if everyone knows the story by heart, then you don't need to resort to writing down as much. If everyone can tell the story, knows the story well enough, then you begin to live & breathe it without thinking about it, without having to go back & check with someone else that you've got the plot right.
This, of course, all saves time & effort. It saves the project from going back to rewrite the story as often, because you tend to get more of the intent early on, even if you don't get all the details. You can even learn to draw more out of the story teller to fill the gaps of what makes a good story. If everyone is used to listening to stories & then retelling them, then they'll know how good each story is, & how easy it will be for them to tell that story, & they will make damn sure that they get the full story as soon as possible.
Nobody wants to waste their time hearing that someone has a story about a walrus, & then a week later being told that it smokes cigars & eats oysters, then a week later that he has a friend who's a carpenter, & then you eventually get to the point of there being a white rabbit & a little blonde girl - but much, much too late.

Tell the story early & often. Rehearse it, find the holes in the plot, listen to others telling the same story. Develop a story culture. Develop a team culture. Develop product sense. Save dollars.