olive oil has a low smoke point, so if you heat it too much for too long, it starts to breakdown and smoke, and you might lose some flavor. that's why high-quality olive oils will say "cold-pressed", they extracted it without heat so the flavor is retained. i never go past the medium setting on the burner when i'm heating it alone, but i might raise the heat once i add the food, because the temperature usually drops to an okay level when you introduce food. it's only something to worry about if you are heating oil by itself, i think
https://en.wikipedia.org/wiki/Smoke_point