Will someone explain something about Facebook apps to me?

[A]

I will see a link pop up from a friend on my news feed, so I click it. As it turns out, it's an app. A few of these Facebook apps are"Pcture of the Day and the Excedrin headache contest. What I wonder about is the "Request for Permission" message that says the app can access my name, profile picture, gender, networks, user ID, list of friends, and any other information I've shared with everyone. Why do apps have to do this? I don't want to actually *use* an app. I just want to see what my friends are up to with them. Why is it all or nothing with these things? Someone, somewhere is gaining some kind of advantage over these. Is someone making money? Is it a sort of sponsorship thing where a company pays money to Facebook to allow it to have all kinds of access to someone's profile which can result in friends getting spammed?

I just want to know the basic premise of apps and why they have to be granted all this access to stuff on your profile.