Why do some investors have their primary residence as a rental ?

Hi Guys,

I am curious as why some investors live on a house and have the legal class a primary residence ? 

Is there a benefit ?

Does it help with taxes ? 

Are they able to qualify for more have that property as a "rental" ? 

Has anyone came across someone with their primary residence as a rental and asked them why they have it like that ? 

I have came across many investors that have their property as a rental when they are living there