I had so many problems I reverted back to iPhoto and continued to use iTunes to sync all my photos to my iPad and iPhone.
I tried the migration one year ago when Photos first came out on the Mac. I have a fairly large Photo Library (~12,000 photos about 70GB) that I finally converted from iPhoto to Photos. The support person I spoke to seemed very certain of this. They maintained that this setting would cause the full-res version of the photo to stay on the device and be uploaded to iCloud. I contacted Apple Support and their response was that 'Download and Keep Originals' only applied to photos taken on the device. Eventually the photos are copied from iCloud to your iOS device if the 'Download and Keep Originals' setting is on.
Thank you LACAllen! D espite what Apple Support told me you are correct.
