Not all advice out there is complete!
Always use really ripe tomatoes for preparing tomato sauces as they are sweeter and fuller in flavour. Using ripe and naturally sweet tomatoes, means you do not need to add any sugar. I know that most recipes that make any tomato sauce always advise you to add sugar. This is not always true. Unripe and sour tomatoes will need help with a bit of sugar, but ripe sweet tomatoes are naturally sweet, so adding more sugar throws your recipe off balance.
This sauce is the base for many recipes and is very handy to make in advance and freeze.