alt Hacker News>> Same reason that "Pretend you are an MIT professor" or "You are a leading Python expert" or similar works in prompts.
This pretend-you-are-a-[persona] is cargo cult prompting at this point. The persona framing is just decoration.
A brief purpose statement describing what the skill [skill.md] does is more honest and just as effective.
I think it does more harm than good on recent models. The LLM has to override its system prompt to role-play, wasting context and computing cycles instead of working on the task.