Sauteeing the rice for pilaf causes the starches on the outer shell of the grain to 'gellate'--they take up ambient moisture, and form long chains between each other, giving a firm, independant structure to each grain. the liquid added to the pilaf provides a medium for shorter chains of starches to leave the grain, which allows the rice to bind to itself---so it's mouldable, etc. basically, sauteeing the rice beforehand allows you to have distinct rice kernals that adhere to each other for presentation, while giving you a bit of leeway--slightly overcooked rice will still seem perfect if sauteed in oil before adding water, because the outer parts of each grain are a little firmer because of the sauteeing.
Sautéing gives the rice a slightly toothier texture and helps the individual grains maintain their integrity. If you sauté long enough to colour the rice, the flavour will be changed; whether that's a good thing is up to you and your palate.
Have never heard of sautéing uncooked dried pasta but would imagine the effect is similar.
There is a Mexican dish called Fideo Soup. The first step in making it is to saute broken spaghetti or angel hair pasta in olive oil until browned. Then, you typically add onions, garlic, chipotle chiles, chicken stock, tomatoes and cilantro to make the soup.
It's kind of like a Mexican Minestrone, with very deep and haunting flavors.