The reasons for adding salt or oil to a pot of boiling pasta are actually different. It is believed that adding oil to the water will prevent the pasta from sticking or cooking together. While this may be true, cooking pasta in water and oil will result in oily pasta that won’t cling to your sauce, making it rather tasteless. To prevent pasta from sticking, just stir continuously for the first couple minutes of cooking. This is the time when the pasta’s starches are released causing it to stick.
Adding salt, on the other hand, enhances the flavor of the pasta. Add the salt either before or after the water begins to boil. Many Italians believe that pasta water should be salty like the sea, so be generous with the salt. Don’t worry about over salting; the pasta will only absorb so much and the rest gets thrown out with the water. Your sauce thanks you.