The computer can only give you a code. It will not tell you what is wrong. Example, you can keep replacing the oxygen sensor as often as you want, but wouldn't it be better to actually find out what is actually fouling the O2 sensor?

Ganun din ang codes. Even top ASE-certified mechs will tell you that. Codes are precisely what they are. A bunch of numbers. You will still have to exercise good clinical (mechanical?) judgement as well as corellate it to the symptoms the vehicle is manifesting to make the correct response. Sure you can follow all the algorithms (it took them almost a month to fix mbt's venture due to this). But it would be nicer if you actually knew what usually goes wrong with a particular vehicle and check those areas first.