Here's the thing: at first I thought the 2nd burner could generate even more heat. However, this is only minimally true (e.g. for pizza). The smaller burner is mainly intended for low cooking.
With the large burner on the smallest flame, the lowest temperature is +- 180°C, which is too hot depending on the grilling project. Then the smaller burner is used.
NB I recommend buying the cast iron grill. It simply works even better.