I think the only way your find the answer is ask jay z himself. Anyway, there are some common reasons to wear sunglasses. 1, people wear sunglasses for looks. Most of people think such black sunglasses can make them look cool. 2, wearing sunglasses can also shield their eyes especially in sun. Sunglasses can reduce strong light and prevent UV rays. 3. some famous people wear sunglasses for disguising because they don't want to be recognized in public.
It is said that the sunglasses Jay Z wears is ray ban sunglasses. As a famous star, he may want to look cool and special when wearing the sunglasses as an accessory. It is his fixed style. However, the sunglasses can be used to protect the eyes from the strong sunlight.
Well, generally speaking, there are two reasons people will wear sunglasses. The first one is that he wants to protect his eyes. As we know that sunglasses are designed for people who like doing activities outdoor. By wearing sunglasses, it can protect your eyes from the UV rays and strong sun light. Also, it can avoid some eye infection. On the other hand, he maybe wants to look cool and fashionable by wearing them. Nowadays, there are many famous stars who do not have any vision problem, but they still wear sunglasses to make them look cool. This is a new fashion.
Well, as far as I know ,Jay Z is an American hip pop star who is famous for his cool music. Actually, his real name is Shawn Corey Carter. You should understand that by wearing sunglasses of bold design, they will appear to be cool and mysterious. Along with his hot dance and style, he really won a lot of fans throughout America. It is not uncommon for those stars to wear sunglasses anyway.