I know that in Northern New Jersey where I grew up and in many of the outer boroughs of New York City there are usually a lot of muti family houses. These homes can house three or even four families.
Usually there is an apartment on each floor and there is a separate entrance for each tenant. It is ideal for a live in owner because the owner could have one of the apartments and can rent out the other units in order to pay the mortgage and since there is a separate entrance for each unit there are no privacy concerns.
In a lot of urban areas you will either see multi family homes or apartment buildings. I liked living in a multi family home when I was a kid because it was more comfortable than an apartment building and I had more space.
A lot of investors look to these types of buildings because the more units that the structure offers the more lucrative it would be from an investment standpoint.