A feature that marks out a chef's cookery book from one written with the home cook in mind is the instruction to de-seed tomatoes. People in professional kitchens may be comfortable with throwing away half the vegetable (fruit, if you like); to the home cook, it seems both fussy and wasteful.
There is a case to be made for throwing away the seeds and jelly if you are incorporating the tomato in a sandwich. You might not want the juice to dilute a salad; but in that case the better option, in my view, is to fold in the tomatoes at the last minute -- or to rest them on top. Perhaps you do not want seeds in a sauce. You might sieve them, retaining the jelly; but surely that is a ridiculous effort.
I am delighted to see that Harold McGee, the food science guru, endorses my laziness. Here, he reports on some research prompted by Heston Blumenthal: the researchers found that the jelly of the tomato contained more flavour than the flesh.
Here is an easy tomato sauce, the method for which I read about in one of Nigel Slater's books. Soften a chopped garlic clove in a tbsp of olive oil; throw in four chopped tomatoes with a little salt (if the tomatoes are unripe, you might add a tsp of sugar), and simmer until the tomatoes have broken down and the sauce has thickened. Pass the sauce through a vegetable mill. Check the seasoning. If the sauce seems thin, simmer it for a little longer.