Problem 1: You have a multi-story building or multiple rooms within 20 meters of each other. You're going to hear cross-talk regardless of walls. This can make conversations harder to follow for RPers, and means that you have to spread sky platforms and such out more for privacy.
Problem 2: If your sim is not sliced into plots, you may run into issues with users camming into private spaces, which can lead to all sorts of nonsense and drama.
Solution:
Similar to how reflection probes work, let us create a cube, scale it to fit a room, click a checkbox and make it behave similar to the "Avatars in this parcel can see and chat with avatars on this parcel" option on parcel control. User can choose "see" and "hear" separately.
With this, sim owners can give users with private homes on their sims actual privacy, and can reduce confusing cross-talk between closely placed rooms and skyboxes can be put closer together for better efficiency.