Rough math... let's say a doorman costs $200/day ($70k/year). 20 units in the building. This would amount to $10/day/unit and thus a rent increase of $300/month for everyone.
For a one bedroom rental, that would represent a 15% increase (on average) for rent increase (based on https://www.apartmentlist.com/rent-report/ny/new-york ).
Note that the long term sublet isn't necessarily a problem - it's the situations where someone is renting out their apartment for less than 30 days and are not occupying it themselves during that period of time.
So now that the property owner is going to be issued a violation if there is an illegal short term rental, how does the property owner prevent that? Note that it is legal to rent out a bedroom of a 2 bedroom apartment on a short term basis if the person who holds the rental lease is there the entire time.