Nice post by Scott Sehlhorst at Tyner Blain on splitting user stories:
User stories were created as lower-overhead use cases that served to better describe chunks of valuable software that could be rapidly developed, delivered, reviewed, used, and improved. Writing user stories that undermine that intent – rapid, valuable, incremental delivery – is a bad way to write user stories.
In particular, good user stories are about the persona, not the product. Or as Scott puts it: "The right approach is to first solve all of the problem for a subset of the users."
Alas, many of the "roles" definitions we see are not personas but vague titles. "As a provider of IT support..."?? Man! That isn't specific! What kind of IT support? Linux, Mac, Windows, mobile? What kind of organization is supported? Large business, mom-and-pop shop, family, everyone who has met a member of my family?
Agile is supposed to help you make better products faster. Focus on personas and their problems and a lot of the rest falls into place.