Why blanche tomatoes?

Answer 1

Blanching tomatoes makes removing the skin very easy. In many recipes, the skin of the tomato would slough off during cooking. This would leave tight string-like curls of skin distributed throughout the dish - they get stuck in teeth and may present a clash of textures.

If life seems too short to blanche a tomato, consider using pre-skinned canned tomatoes instead; they cook in fractionally less time and are slightly stronger in flavor, but they take much of the boring legwork out of cooking.