Have you ever grated a ripe tomato? No matter how many times I do it, I think it's thrilling. The best tomatoes for grating are so juicy and fat they treaten to burst in your hand even before they meet their grater.
Then all you do is halve your tomatoes and run the cut sides through the large holes of a box grater (over a bowl!) until the moist flesh is scraped away from the skin (discard skin or use it for another purpose though what that might be I can't imagine). Then use the pulp for sauces. No bits of tomato skin in the pan and grating is much easier than chopping wet, squishy ripe tomatoes, cubes of which inevitably fall off the cutting board and onto the floor with a splat.