Different types of rice have different qualities when cooked.
A long grain rice has less surface starch and remains whole and doesn't stick to other grains readily. However, it is no good cold as it becomes hard and crunchy when cold but is fine if reheated. Great for things like steamed rice and pilaf but not so good for a cold rice salad. Chinese restaurants use leftover steamed rice (long grain) to make fried rice.
Medium grain rice has more surface starch. When cooked, that starch dissolves and creates a creamy sauce with the liquid used to cook it. Great for risotto. Also good cold as it stays soft.
Short grain rice is sticky. It clumps together and can be shaped into fingers or pressed onto seaweed to make sushi and it will hold its shape.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan