This had two side affects.
1) People were afraid of being fired. You could come in one day and be sent home that afternoon without ever having any idea that you were under-performing. You'll hear Netflix employees talk about the "Culture of Fear".
2) In a meeting with my team Patty said "We are your co-workers, not your friends." `The idea being, you don't make friends at work because you might have to fire that person one day. It was really strange, people were very guarded and almost never talked about their lives outside of work.
PIPs protect employees from the constant fear of being fired. They require managers to give an employee negative feedback. Without them, managers can take the easy route and never have the uncomfortable conversations.
#2 made life really hard at Netflix. The majority of my friends come from my co-workers. You spend more time with them than most other people in your life. Some teams ignored the company culture and became close friends anyway. I think the correct thing to do here is to expect your managers to be adults and do the hard thing. Fire your friend.