The idea is supposedly to "get inside the heads" of the target user. This will lead presumably lead to some sort of intuition about what their needs are and how to market to them.
TFA sheds no light on the unique advantages offered by detailed personas.
The idea is to get the user in your head as a real human being not as an abstract category.
If you design for "User who needs product X" then you come up with different design than if you think about "Jim wants to buy a gift for his nephew's birthday, he is late, the birthday is tomorrow." You can better come up with ways to support Jim. You feel the importance of a speedy delivery.
You can also think about new features like asking this user if he wants a suggestion mail sent to him for next year (minus two weeks), that has present suggestions for kids that are 1 year older.
Now I just made that up, and it might be a terrible idea, but the point is, that you could never come up with something like that without a persona.
Hmmm. My product has "this cluster of users" vs "that cluster of users". But we really don't attempt to imagine their home-life. Or race or sex or orientation. Just what they are into feature-set wise.
EDIT: I think we call them "User-Type-A" and "User-Type-B". That doesn't sound very sexy - but it helps us prioritize feature development (esp. since "User-Type-B" never pays for anything - those features come last. But the non-paying user type is the most winge-ey - I've never figured out how that could be - but they are)
TFA sheds no light on the unique advantages offered by detailed personas.