"custom.css" for inherited themes - why is this the preferred approach?

Wouldn't it be easier, cleaner and faster to just copy all the scss files over to the child theme and make changes in the respective files?

But then if a fix comes out that addresses a bug, or new functionality is added to the theme you based your 'copy' on you would have to manually copy/merge those into your theme. The choice is yours! :)

Thank you for your fast answer and awesome work :)