Nowadays, with my mother-in-law staying with us, as you can imagine there are a lot more closed doors. All the bathroom doors are always closed, and now we all sleep with bedroom doors closed as well. The first night my mother-in-law left her bedroom door open, but I made M close it for her the next night. Any sound buffer is a good thing, I think, whether it's needed or not it can't hurt. We've brought out the good ol' baby monitor so we can still hear the baby.
It seems like such a small difference but it's a big impact. It's an existential thing; before the house was free-flowing, open, and our little family was never cut off from each other. Now it's stagnant in some areas and we spend a lot of time cut off from each other by all of these doors.