For the human. Videos are way more interesting to most people if there's an audio track of some kind. Anyone who doesn't like the sound can mute it.
Less processing really isn't relevant. CPU is cheap. Yes, audio does take some additional space & network, but it's practically nothing compared to the space required for a video. So if you're making a video anyway, add some sound and make it interesting for the human who's viewing it.
Not really picking sides but the one thing I hate with music is that if I for any reason would not like to listen to it. Maybe I'm already listening to music - maybe I don't have my headphones on and don't want to disturb anyone else (or don't have speakers). Or I'm on a laptop/phone where the speakers are just terrible.
If I press the mute button I will not know if I'm missing out on some important commentary.
There should be a standardized way to convey that the audio is optional and doesn't directly relate to the video. To be fair this also applies to videos without sound (how am I supposed to know there is no sound unless I've watched the whole thing?) - though with the advantage that one can leave it unmuted and at least detect if someone starts talking.
For the human. Videos are way more interesting to most people if there's an audio track of some kind. Anyone who doesn't like the sound can mute it.
Less processing really isn't relevant. CPU is cheap. Yes, audio does take some additional space & network, but it's practically nothing compared to the space required for a video. So if you're making a video anyway, add some sound and make it interesting for the human who's viewing it.