Corn starch breaks down when heated too much, i.e. after it thickens, continued heating makes it thin again. That's why when you make gravy using corn starch as the thickener and reheat it the next day you have to add more corn starch. It also does not stand up well in acidic environments. That's why tomato sauce recipes use flour if a thickener is needed, and why fruit sauce recipes call for tapioca pearls or tapioca flour.
Modified corn starch does not break down with continued heating and it does well in acidic sauces. Like regular cornstarch, it becomes clear when heated with water, so it is preferred when thickening fruit sauces as the sauce will stay transluscent and not mask the fruit's color like flour will.