All your devices backups (iPhones, iPads, Macs, any other Apple Device), all your pictures and videos, and all of your saved documents. For backups it DOES conserve space it's not a "time machine" style backup, just the vital stuff gets backed up. Copies are NOT made for your apps for example, which the system knows can just be downloaded again. Apple will tell you IF you need more space. Generally the more devices you have the more space you will need. For example I was fine, BUT now that I have an iPhone, 2 iPads, a Mac Book AND an iMac I need the extra storage and pay .99 per month. Small price to pay for the piece of mind, in knowing you are safe in the case of disaster!
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