One: turning on iCloud backup sets off a warming on iOS saying that this action stops iTunes local backup.
Two: your notes as backed up to iCloud will only restore if your iPhone is stolen, dies, etc. But if your notes get deleted or get lost AND immediately this is propagated to the cloud, they're gone. Their deletion will propagate to your iMacs, MacBooks, iPads, etc... You may just see them disappearing and say Doh! The only way to call that backup would be KNOWING that your notes on one device are gone, then immediately cutting internet from all others and rewrite them one by one (good luck if you have hundreds), because even if offline you'd not be able to say store and restore....
Apple, we love you, but this is ridiculous. Even more so now that you're big and can afford solutions.