About enabling iCloud Drive, Apple have stated following until Yosemite leave it's beta phase:
After you install the OS X Yosemite Beta, you will be asked whether you wish to upgrade your account to iCloud Drive. If you choose to upgrade your account, iCloud Documents and Data will be disabled on devices that are not running OS X Yosemite or iOS 8. iCloud Drive will be available only on other Macs using the OS X Yosemite Beta and iOS devices running iOS 8. If you want to continue using iCloud Documents and Data on devices with earlier versions of OS X and iOS, you should not upgrade your account to iCloud Drive.