Scenario: I'm at work and I have a date night planned with my wife. The kids will be staying home to see a movie and it's my job to find something for them to watch. "Hey, I'll find something in iTunes", he says. So I do, and I buy it. And now, the iTunes app on my phone is trying to download a HD movie to my phone.
Maybe, just maybe, someone would want this to happen. Maybe they are near an Apple TV where they can play the movie back to a bigger screen. Maybe they just have to watch The Matrix again and are okay with seeing it on their phone. But surely, the majority of people buying movies on their phone would prefer to purchase it then, but view it later.
I really don't get why Apple would assume to download something of that size to my phone without asking me first. What's worse, the last time this happened, I saw no way to STOP it. I had to let it finish downloading the entire movie before I could delete it from my device.
This is easy to fix: ask the user if they want to download the media once the purchase has been made. And if you have a Mac at another location that watches for new iTunes purchases and downloads them, then it would pick up and download the content so the kids at home can see the movie without Dad having to authenticate in iTunes and download it manually.