I looked and this hasn't been brought up yet. Certainly the mouth-feel, or texture of the pasta is part of the edating experience, but so is the flavor. As was stated, different pastas have differing aboilities to stick to various sauces. But there is one more difference. Lets compare rigatoni, or penni with macaroni for instance. Both have a hole in the middle. But the wall of the pasta is much thicker in both the rigatoni or penne that it is in the elbow macaroni. The pasta noodle has a sweet, starchy flavor that plays an important role in the recipe. When serving macaroni, the pasta serves mainly as a vehicle for the other flavors and contributes genty to the expereince. You can hardly even taste it in dishes like macaroni salad, or tomato-based sauces. While the flavor of the other two mentioned is more robust and exerts a strong influence on the overall flavor of the dish.
Think of the last lasagna you ate. Lasagna noodles are thick, with a robust flavor that needs to stand up to the other very flavorful ingredients in the meal.
So, to summarize, different shapes allow you to taylor the pairing of noodle and sauce, condiments, or oils, , to the taste, texture, and ability to stick or remain seperate from the other ingredients in the dish.
And besides, have you ever tried stuffing a macaroni noodle? Go 'head. Try it. Just use a tiny spoon.
I'd much rather stuff a manicotti nodle myself.
Seeeeeya; Goodweed of the North