Summary
With Photo Stream, every single picture saved in Camera Roll is uploaded to the iCloud server and made available to all of your devices. Then, you can share these pictures with your friends and loved ones by creating a Shared Photo Stream and let them comment or like the pictures. You will have no more hassle sending images via e-mail or sharing using USB just for showing the pictures to the people you want.
On the other hand, iTunes in the Cloud helps you to access and redownload all your purchased content without extra charge. Once you have bought a movie on your iPhone, you can enjoy it later on your Mac at home. Thanks to the Automatic Downloads feature on iTunes which is a part of iTunes in the Cloud. Same thing happens to your other purchased contents. Even with iTunes Match, you can have your iTunes Library with you everywhere, since it's already available on the iCloud server.
