Close your eyes with me. (Now open them because it's hard to read with your eyes closed.)

You're going out of town for the weekend, leaving your dog/cat/baby/orchid in the care of a seemingly responsible adult.

Do you:

Type up a detailed, by-the-minute schedule, complete with an FAQ section and a diagram of your home's exits;
Write a lengthy note describing the basics and emergency contacts; or
Smack a Post-It on the counter with a hastily scribbled "good luck"?
There's no right or wrong answer here, but you'll likely get wildly different outcomes based on what you choose.

It's the same with a content brief: how you set it up and what you include determines how well the resulting draft will meet your expectations.