What is the purpose of the alternative street parking in New York City?

Question

What is the purpose of the alternative street parking in New York City?

Answer 1

My friend, so the street sweeper can sweep the street. If you read the no parking sign on one side of the street, you notice that you can not park your card on a certain day. You will have to move your car to the other side of the street, otherwise you will get a ticket, or even worst a tow.

Good luck

Answer 2

Yeah, Native New Yorker is right it's so  they can clean the street on the side where the cars aren't parked