User story is a popular mechanism used by most agile methodologies to communicate user requirements. Actually, this is only partially true. User stories are meant to be a placeholder to initiate an early conversation between the product owner and the team on key hypotheses so that a quick validation of them could be done to refine/confirm/reject our understanding of what the customer really wants. To that end, user stories are not anything like the requirements of yesterday – they are not even remotely meant to be complete/comprehensive and so on.
The reason user stories (and not ‘well-formed’ requirements, if that is ever possible) makes sense is because we human beings are not experts in following the written word, and are likely to misinterpret requirements even when they are explicitly written down, especially when the communication is a one-time event and not an ongoing process. (if you don’t believe this, just visit this interesting site http://www.cakewrecks.com/ that celebrates real-life examples of how something as simple as icing on the cake can go horribly wrong despite really simple and absolutely clear instructions!). And we are talking about building complex mission-critical systems that must operate 24/7 with top speed and efficiency. If only the written word could be consistently understood by the receiver as intended by its author…
On the other hand, if there is a continuous two-way dialog between the product owner and the agile team, such purposeful brevity leads to curiosity which then leads to a constantly improving and better shared understanding that refines as the product gets developed incrementally and gets periodic user feedback.
The key benefit of user stories is that instead of waiting for weeks (even months!) to get a fully-bloated and rather unprioritized PRD which is supposed to have fully-baked requirements while the development team sits idle all this time, is that identifying highest priority user stories and using them to develop a prioritized product backlog allows the teams to get started much earlier and start developing features which could then be put out in front of customers to get real feedback (as opposed to individual ‘opinions’ that might/not best guide us in an uncertain environment). This is especially important because in the past, when the world was little less complex and much more underserved. I purposefully use this term ‘underserved’ because it is not that people have suddenly become much more demanding about what they like or not, but were just told there were exactly three carmakers to choose from, or just two operating systems to choose from, and so on. However, with rapid advancement of computing paradigms and constantly lowering cost of ubiquitous communication devices, they suddenly have the opportunity to demand what they want, and hence classical ‘forecast’ models of requirements elicitation, design or production (at least in the manufacturing sense) don’t work so effectively as much as the newer ‘feedback’ driven models that allow for developing key hypotheses (and not hard requirements carved in stone) which could then be quickly and cheaply delivered as ‘done’ features so that customers could tell us if they like them or not. Based on such valuable customer feedback, the team could iterate to either refine the feature, or to pivot, as the case might be. In the past, this might take the entire product gestation cycle, by which time, many, if not most, things might have undergone significant changes, and the entire development costs being sunk by that time, not to mention complete loss of any window of opportunity.
As Facebook says – Done is better than perfect. User stories allows developing a small slice of the product without really perfecting the entire product, but facilitates the process of validated learning that eventually helps develop a product with much higher chances of meeting customer needs.
In today’s world, you probably might not have the luxury of having investors wait multiple years for an exit, or customer waiting several quarters for a perfect product when the competition is willing to serve them faster (even letting them lay their hands on an earlier version and give feedback thus making customers a co-creator of the product), or employees working month after month without getting any meaningful feedback from customers. And we know that absence of any feedback eventually leads to erosion of trust. Incremental product development could help you bridge such trust deficit by delivering highest value to customers early and periodically, and user stories might help you get your project a quickstart.