You'd clear the codes & if the problems are still present they would come back, generally if you use the disconnecting of the battery method you also erase the KAM
(Keep Alive Memory) which stores adjustments the EEC has made for your particular car.
You would remove any stored codes and reset the parameters that the computer has "learned". Reseting the codes can cause a minor loss of smooth performance until the computer "re-learns" the parameters needed for proper operation.
Resting the computer will not fix any defective components. It is a good idea to reset the computer when you have cleaned, changed or adjusted any sensor.