If you think of sound as lighting and give it the same attention, then you'll understand the complexities of good sound.
Whether running a dialog interview of a full fledged dialog movie production you'll face the same challenges.
Obviously the principle characters need to be understood cleanly and professionally, but ambient sound (if there is ambience beyond a studio) has to be recorded with the same attention, which usually requires multiple recorders and recording ambient sound wild so you can place it in as required.
This usually requires multiple recorders, and/or multiple tracks so you can separate sound and place it into the edit with logic and art.
A professional sound technician can be a lifesaver though technician is probably no the right job description as someone who monitors sound must listen for the art, tonality, inflection as well as the overall quality of the take.
We now see hundreds (thousands) of new videos that are shot with competence, though the sound is dismal. You can here click settings on the camera, ambient noise that interferes with the dialog and ambient/foley sound that doesn't really match the scene.
If your doing documentary work, you may get away with the "realness" of this, but usually it's just a distraction and with the new versions of dslrs, even the new prosumer sound device, there just isn't enough sound inputs to record proper multi channel sound.
3 are a minimum, 4 is preferable and even if you get a clean take, with multiple subjects you still stand a great chance in doing it again in looping/dubbing.
Though these new hand held sound devices work well, they don't really zoom properly and don't replace a person dedicated to sound on set, will not replace a sound edit for the final piece.
Sound is important and just like a good to great camera will never replace a visual artist that knows how to work it for the best effect, sound has the same requirements.
P.S. One of the best sound devices is the old Canon XL1 standard def camera. Mounted with a good zoom mic, the sound quality the camera can record is simply amazing. It may sound crazy to run a separate camera as a sound device, but it does work and allows you to frame and zoom the sound in a visual manner.