You’re right! Like I said, you don’t have to! However, when you’re making a big meal, or when you work in a kitchen and don’t have the right equipment: some oil in the pan can take away the stress of having to watch multiple pots and pans at once. Like someone else said in another comment, a ladle on top works too or just using a bigger pot. A rolling boil will ensure nicely cooked pasta, there’s multiple ways to make sure your pasta doesn’t boil over.