You need persuasion when requesting a favor from someone you don't know because
a. expert opinion and statistical data are not enough.
b. the reader needs sufficient evidence to make an informed decision.
c. you want to make the desired action as clear and easy as possible.
d. the reader is getting no tangible benefits from granting the favor.
e. this is a routine request that is likely to be granted automatically.
Answer: the reader is getting no tangible benefits from granting the favor.