Telling the model what perspective to take.
WHAT IT IS
Specifying a role or perspective for the response.
"Answer as an experienced accountant explaining to a small business owner."
WHY IT HELPS
It sets vocabulary, depth, assumptions and register in one instruction.
WHAT WORKS
Roles describing expertise and audience together "Explain as a teacher would to a beginner" "Review this as a sceptical editor" "Assess as someone who has to implement it"
WHAT DOES NOT
Elaborate personas. "You are a world-class expert with twenty years of experience" adds nothing over "answer as an experienced practitioner".
The elaborate version is a common recommendation and the improvement is marginal.
WHERE IT GENUINELY HELPS
Getting criticism. "Review this as a hostile reviewer" produces different output from "what do you think".
Setting depth. "Explain to a specialist" versus "explain to a beginner".
WHAT TO COMBINE IT WITH
The audience. The role sets the speaker; you still need to say who is listening.
WHAT IT CANNOT DO
Give the model expertise it does not have.
A role does not make the output more accurate.