[another-dave]

IMO, the format is meant to do two things:

* By having a premise, it forces you to question its validity up front (before any development work is done), getting rid of ambiguities early and having a shared understanding between business and technical team members (rather than the developer implementing what they think is a better solution, the product owner being unhappy with the outcome & only finding this out at the end).

* Using the format of "As a <type of user>, I want to <use a feature>, so that I can <achieve some value>" forces you to think about what user (customer/website editor/back office) gets what specific value (faster/cheaper/less error prone) from implementing some feature. By following the same pattern it makes it easier to compare unrelated areas.

I don't think the format is sacrosanct, but it's like any constraint you put on yourself (e.g. coding conventions) — if you find it hard to make a story work in that format, it's an indication that it may not be properly understood it really bringing value.