I would imagine it's the other tenants in residential buildings that are letting their finger do the walking as they used to say. Especially if they have families or the wives dont want their husbands getting lost when they go out for loaf of bread, stick of butter, etc.
In commercial buildings, who knows. I remember waiting outside a providers "office" once upon a time in the hallway in a commercial building near Herald Square. It was a double office. The main office had a solid wood door but there was a second exterior entrance from the hallway from its adjacent office. It had a glass pane that was distorted so you couldnt really see what was behind it clearly. But it wasn't a particularly sturdy door. So I'm waiting and I'm too early and I'm standing by the second door and I hear some thumping around and a girl moaning ever so softly but loud enough to hear in the hallway. Squinting thru the glass, I could see the girl was getting double teamed by two lucky gentlemen; it was their shadows more or less in appearance but i wasn't having a hallucination. Th term for what they were doing to her is called a spit roast if I recall correctly.
I stuck around for a few minutes to fulfill my voyeur fantasy and left before I got caught by another tenant on that floor. This office was practically opposite the men's room on that floor so there could have been man traffic at any time really.
She eventually moved from that office space and later retired. A bunch of other providers and legit therapists have been there since.