Why can't couples sleep together when they go to a friend's house? What's the significance of Feng Shui?

There is an old saying: "When a pheasant goes to bed, the family is ruined." "When a son-in-law goes to bed, the family is ruined."

It is said that it is not good for the boys at home, and the married girls go home and share the same bed, which affects their brothers. I guess the guests influenced the status of the Lord.

Still from health, respect, privacy ... Anyway, if such a thing happens to me, it will be a little uncomfortable psychologically. What kind of friend does this have to be?