Edit: Funny how the sole argument for why annoying sounds should be on by default is downvoting. I rest my case.
Why not? Sounds are a subtle and quick indicator that something went good or bad. And if you find a particular action too repeating you can turn that sound off.
It's not subtle when all if the desktop plingplogs all the time about everything. Those things should be off by default and turned on only on demand in the accessibility settings for the visually impaired.
If it doesn't matter for some and it's an annoyance for others, it should be off and visually impaired people who rely on that can turn it on (unless their screen reader tells them anyway, then a second sound is useless for them as well).
Will be fun to try this when it comes. Maybe at the same time as the new Cosmos desktop from system76...