yeah, i don't know anyone who would want to dump 6 quarts of pasta water in their tomato sauce. i think the "point" of the question, is in the question itself.
the reason for salting the water is simple: more coverage because the salt dissolves in the water. if you salt the pasta when it's done, the salt doesn't always break down, and the flavor is inconsistent - some bites will be saltier than others. as a rule, to make good pasta, you have to generously salt it. so many people get their sauce to the perfect flavor, then toss it with the pasta and it's bland because they didn't season their pasta enough