When should or shouldn't you use pasta water? Every sauced pasta dish recipe I ever read calls for using the water in which the pasta was cooked for the purpose of thickening the sauce, as the water contains a lot of starch which helps the pasta adhere to the sauce

In this recipe, this step is skipped and the pasta is added without any water/starch

What was the reason for not using the pasta water? Or in other words, when should you not want to add pasta water? (other than in cold pasta dishes like salads)
The simplest answer is, if you need to dilute the pasta sauce, it’s better to use the cooking water.