Olive oil and vegetable oils (sunflower, canola, soy) differ significantly in composition, flavor profile and health effects.
Extra virgin olive oil is rich in monounsaturated fatty acids (oleic acid) and antioxidants. Most vegetable oils contain more polyunsaturated fatty acids, which are less stable when heated.
In culinary terms, olive oil is a flavorful ingredient, not just a cooking medium. Vegetable oil is neutral; olive oil adds its own character to every dish.