Good sound is more important as a good visuals. The audience can tolerate blurry pictures as long as there is clear sound.
Using microphones to capture audio clips adds a lot of production value to a film project. Getting audio right can be time consuming and technical, but it is a critical component. The production mixer is responsible for sound recording during production.
Usually, most of sound designer’s work is done during post-production.
“Sound design is how filmmakers flesh out the aural world of a film to enhance the mood, atmosphere, and/or tone.” --Sam Kench
Sound design often include sound effects (SFX), mixing, Foley sound design, dialogue, and music. Sound design is the final and most important element needed to create an immersive experience for the audience.
Remember, a good film is a powerful unified experience combining sight and sound.