What is the point of a hooded sweatshirt vest?

Clothing provides protection from the elements

For people who don't like a too-cool breeze in the shoulder seasons?

To conceal

Or a sleeveless turtleneck!

It is quite functional, unlike, say, a watermelon costume.

People hide inside of them, which means a hooded sweatshirt can mask one's identity from security cameras. Most bars and nightclubs don't allow 'hoodies' to be worn inside the premises because most robberies are conducted by thieves who wear hoodies to avoid security cameras.