Some businesses by their nature demand isolation from the intrusive sounds of the outside world. Concert halls and theatres would forfeit their enchantment for audiences subjected to noisy reminders of the external world of lobby and street. Recording studios cannot function with even miniscule sound intrusions from the outside.
Other facilities need to shield common workspaces and office employees from the distractions of resident noise emanating from the HVAC plant and other heavy equipment rooms. Virtually all types of commercial buildings need offices equipped for private conversation. And the need for absolute confidentiality is a modern byproduct of expanding national security operations.