You cannot profit legally from a sublet. Some leases may allow you to rent it out for the same amount monthly, or even partially, but you are never allowed to charge more than you pay. AirBnB is actually pretty illegal in NYC, at least the way most people use it.

That is not exactly true. If the apartment is not rent controlled there aren't restrictions on how much you can charge. However, you are supposed to do sublets above board with a real lease agreement and the landlord's knowledge.

If it's a rent controlled apartment you are prohibited from charging more than the fair value of the room. If it isn't rent controlled, anything goes.

Most people, myself included, who rent in the city have all of that laid out in the lease agreement. Most landlords probably wouldn't know either way unless they are coming by the apartment often. In either case, it's not a huge issue in the city.

* Most landlords probably wouldn't know either way [...] it's not a huge issue in the city.*

I don't know about that. If it's not legal then I think people should know that, whether their landlord is aware or not. Same as avoiding paying tax- you could get pretty badly burnt.

I wouldn't liken tax evasion to letting someone use your apartment. I was really just speaking casually about how the situation would unfold. It's also a grey area since this is less of a sublet and more of a micro sublet (akin to letting a friend over for the night who buys you lunch in turn), which complicates the legality of it. Err on the side of caution I guess, but reading your lease agreement is obviously the best thing one can do.