Currently by default when using a video output there is no sound enabled by default. However, this is bad from the user point of view.
There are several examples of new users who have no idea why sound is coming from Blender but after rendering there is no sound. See T50168
# If you are using a video output most likely you will want audio.
# Extra step to take to get audio.
# If you don't want sound you will not have an audio object.
My purpose is to enable a common/ universal audio codec by default e.g. .mp3