I think it depends on the parents. I know people that have parents that get drunk with them/smoke weed with them. On the other hand, there are parents that feel the need to treat their 30-year old children like 3-year-olds and second-guess every move that they make; ready to talk down at them with 'advice.'

If your parents are going to treat you like a child and/or you don't have an open enough relationship with them to feel comfortable bring home a girlfriend / having sex with your wife, then there will be inevitable conflicts.