Anytime you are living in your parent's home after you become an adult (18) is with their permission. Squatter's have no rights, they are there illegally (trespassing) and are not renters or owners to the property. That being said, as a responsible Adult, you should be required to abide by your Parent's rules which can include cleaning, working, and Paying Rent.
As a general rule, you want to pay rent. Paying rent gives you more rights than someone who does not. If you're squatting, you can be seen as trespassing and if you're a guest, the host can revoke your invitation to stay there.