The original Photo Stream service automatically saves your last 1,000 photos or 30 days of photos and syncs them across all your Apple devices. Since Photo Stream doesn't count against your iCloud storage, you might think you don't have to worry about deleting them. However, every once and a while a photo might slip in that your definitely don't want syncing between your devices. If and when that happens, you can easily delete the photo from Photo Stream, and that will not only remove it from all devices, but in the case of the new iCloud Photo Library service, delete it permanently as well.
