For which items should the grill be lightly buttered?

The correct choice pertaining to lightly buttering the grill is that it is primarily necessary for steak and chicken. These items benefit from a light buttering of the grill because it enhances their flavor and helps prevent sticking during the cooking process. The butter adds moisture and richness, resulting in a more appealing finish and texture for these meats.

While grilled vegetables can also be flavored with butter, they do not require the grill to be buttered to the same extent as proteins like steak and chicken. Not all grilled items necessitate this treatment, which is why the other choices don't accurately address the specific needs of steak and chicken.