When to use "use scalar properties for primitive data types"


I’m wondering if anyone can give a plain English explanation for when (or why) I should or shouldn’t select the “use scalar properties for primitive data types” when creating the NSManagedObject subclasses out of Core Data? I’ve tried to get an explanation that gives clear direction out of the book, the forums here, and googling aorund but I don’t feel that I have a firm grasp on why I should be selecting this option, and the benefit to the application.

Any explanation would be very much appreciated as this has been gnawing at me for quite a while!