Renting a NYC townhouse

I don't know what your friend means re: 'rules' but often townhouses are owned by small-time landlords who likely won't have any staff (super) or management company. So if your toilet breaks, for example, you're dealing directly with the owner, who may or may not be terribly responsive and who may then need to call in an outside vendor to repair it. Same can happen in larger, managed buildings but having a good super onsite can help stave off some of these headaches.

Another unrelated thing to consider re: a townhouse rental unit is that the soundproofing tends to be terrible. Since these buildings were originally geared towards single-family use they weren't built with multiple residents in mind. You can expect to hear everything your neighbors are doing.

If it were me I'd vastly prefer to live in a larger rental building rather than a converted townhouse.