If you cook chopped tomatoes with all of their juices, it takes a long time for the sauce to reach the right consistency. By then, the freshness is gone.
It's important to salt the tomatoes before draining them because that helps pull out the water. Fresh herbs, some garlic and pepper will also enhance the flavor.
There's a point of no return when you're cooking tomatoes. A little too much heat, a little too long in the pot, and you lose that sense of fresh ripeness that makes tomatoes so great.