Apple is doing something remarkable (and really smart) with iCloud. For devices running Yosemite and iOS 8, the operating system can optimize local storage by automatically storing large files from photos, videos and other raw data formats in iCloud and keeping a low-resolution version on the device. During the installation, a prompt offers the option of upgrading the corresponding iCloud account to add the new capability, warning that devices not running the latest OS will be iCloud-disabled. The cautionary note here is to make sure that all devices in need of iCloud access are capable of running iOS 8 when it comes out this fall.
Changes To iCloud