Some chefs avoid peeling tomatoes because the skin contributes flavor, nutrients, and texture to the dish. Peeling can also be time-consuming and unnecessary depending on the recipe.
The skin of a tomato contains a significant amount of flavor compounds, particularly those that develop during ripening. Removing the skin can diminish the overall taste of the dish, especially if the tomatoes are of high quality and properly ripe. Furthermore, the skin provides a textural element, offering a slight chewiness or firmness that can complement the softer flesh of the tomato. Nutritionally, the skin is rich in antioxidants and fiber, which are lost when it's discarded. Finally, for certain dishes like rustic sauces or stews, the slight imperfections and varied textures contributed by the skin are considered desirable, adding to the dish's character and visual appeal. Peeling tomatoes is often recommended when a completely smooth sauce is desired, or when using tomatoes with thick, tough skins. However, for many applications, the benefits of leaving the skin on outweigh the perceived drawbacks.
If you're concerned about tomato skin texture in a sauce, consider using a food mill or immersion blender after cooking to achieve a smoother consistency while retaining the flavor and nutrients from the skin.