Fun fact: what that audio guy was describing is called “room tone” and correct it’s used for both patching and as a base sitting under all the other audio elements for the mix (music, dialogue, sound FX) and is a common practice after a on location shoot is wrapped to have the whole set “hold for tone”.

The reasoning being it captures the 3D soundscape of the ambient noise in the space and how those noises bounce off surfaces and people that our ears definitely notice when it’s missing like your post says! The reverb of a small office room and a gym would have very different room tones for example. And an absolute void in audio is extremely distressing and it’s why you almost never have absolute 0dB in a sound mix unless intentional.

Source: work in professional production