Honestly, super practical for anyone who plays in a band and wants to host practice and have their neighbors like them anyway.

Or has a kid who's in the same situation...

All the other ideas get dark very quickly. In addition, CO2 accumulation makes the mind a bit stupid quite quickly, even in an office, so I wouldn’t stay there…

Or just more living / working space.

Say you're in one of many low to medium density areas (sf, suburbs of nyc, etc) and need more living space. Going up is very expensive and causes conflicts with the neighbors (earthquake zone, views); down is even more expensive; building in the yard loses, well, the yard. So going under the yard is not a crazy option.

Particularly in our brave new wfh world where employees now have to pay for their own working space.