By resetting the ECU, the light goes away. But if the fault is there, the light will come on again. It is not like the warning has been suppressed forever.
It is a good test as CEL is known to be easily excitable and keeps turning on every now and then. If you see on the internets the people from modern countries (who have had ECU cars for the last 30+ years) have ll shared there stories of spending endless money trying to find out what the CEL wants to tell them.
Some of them have also ignored the CEL, went on with routine maintenance and still been able to clock 500,000 km without failing emissions tests, without excessive fuel consumption and without any traffic accidents. Remember the best engine check is done by the human in the driving seat, using his/her senses of sight & hearing.
EDIT: Moral of the story: Don't ignore it, but don't let it rule your life also.