More specifically, it has this many:

This, according to a NYC government website, equals 8,660 active shed permits covering 1,959,444 linear feet. And on average, these construction sheds are erected for 493 days. If you've been to New York recently, this will all sound right to you.

I thought I had read somewhere that this has to do with a property tax benefit. Something about if you keep your hoarding up after construction completion, you can avoid immediate reassessment.

But according to some sources, the proliferation of sheds is mostly driven by the city's Facade Inspection & Safety Program, which requires that all buildings taller than 6 floors have their facades closely inspected every 5 five years.

So presumably, keeping these up for an extended period of time is the less costly and less risky option.