Why Is Allowing Tenants To House Non-Verified People Bad?

[Ethan Armstrong]

My wife and I have many discussions about being future landlords, and the one topic we butt heads on is if it's okay to let your tenant have someone live with them for an extended period of time. Her biggest argument is that the tenant is renting the home, so they're paying for it, so they should be able to house a friend or family for extended periods without having them being cleared or verified. 

I made some headway when I presented the fact that the home OWNER owns the house. If someone lived with you in the basement, you'd be rather uncomfortable (to say the least), having another person that you didn't know living down there. That example is slightly flawed since you aren't living in all your rentals. 

I would like help explaining this to her, but I can't come up with reasonable examples or reasons that make real sense. I'm looking for reasons, examples, or personal experience whether good or bad. 

Thanks in advance from a BP reader, and future contributor.