No matter how good a video may look, it can be brought down by poor quality audio. It can be affected by not using the correct equipment or not using it in the correct way
There's times when your audio does not turn out the way you want and while it is always better to get it right in production sometimes it's not possible to re-record. You can send your audio to DRB video and using industry standard audio software and correction techniques many issues can be vastly improved or eliminated all together.
Background hum, background and ambient noise, mild level distortion (clipping)