Like many photographers that insert their SD or CF cards Apple Photos interrupts the download process by auto launching the app. This can be annoying and time consuming.
"But I un-clicked the 'Opens Photos for this device' button."
Yes, but if you format you cards it is interpreted as a new device and defaults to launching the app.
The best way I have found out to deal with this is to change the code using Terminal. This is not as scary as it sounds.
Once in Terminal copy and paste this command.
defaults -currentHost write com.apple.ImageCapture disableHotPlug -bool YES
That's it!! No more auto annoying launch. If you need to change back to the original setting us this command.
defaults -currentHost write com.apple.ImageCapture disableHotPlug -bool NO