When you turn on iTunes Match, Family Sharing, or Automatic Downloads, or when you download past purchases on your computer, iPhone, iPad, or iPod touch, that device becomes associated with your Apple ID. You can associate your Apple ID with up to 10 devices, with a maximum of 5 computers at any time. Each computer must also be authorized using the same Apple ID. You don't need to authorize your iPhone, iPad, or iPod touch.

After you associate a device with your Apple ID, you can't associate that device with another Apple ID for 90 days.