> It's run _before upload to iCloud Photos_ - where it would've already been scanned anyway
Right, so ask yourself, why is it on the device? Why not just scan on the server?
To me (agreeing with much of the commentary I’ve seen) the likeliest answer is that they are confining the scan to pre uploads now not for any technical reason but to make the rollout palatable to the public. Then they’re one update away from quietly changing the rules. There’s absolutely no reason to do the scan on your private device if they plan to only confine this to stuff they could scan away from your device.
Right, so ask yourself, why is it on the device? Why not just scan on the server?
To me (agreeing with much of the commentary I’ve seen) the likeliest answer is that they are confining the scan to pre uploads now not for any technical reason but to make the rollout palatable to the public. Then they’re one update away from quietly changing the rules. There’s absolutely no reason to do the scan on your private device if they plan to only confine this to stuff they could scan away from your device.