True Dave but at some point the scan tool will become a requirement. Plus, you can get the one that allows you to upload performance software.
I get codes way too frequently as I burn out O2 sensors like they are candy. I continue to use them for a long time after they throw the first code (always the same O2 heater ...). So as long as I have the scan tool I can check things like oil temp, coolant temp, inlet air temp, etc with good accuracy. Even O2 to make sure the sensor is actually working and only the heater circuit response is off.