I am attracted to the idea that you shouldn't care how the code you author ends up in the browser. It's already minified. It's already gzipped. It's already transmogrified (real word!) by things that polyfill it, things that convert it into code that older browsers understand, things that make it run faster, things that strip away unused bits, and things that break it into chunks by technology far above my head.
The trend is that the code we author is farther and farther away from the code we write, and like I said, I'm attracted to that idea because generally, the purpose of that is to make websites faster for users.
But as Dave notes, when something goes wrong...
As toolchains grow and become more complex, unless you are expertly familiar with them, it’s very unclear what transformations are happening in our code. Tracking the differences between the input and output and the processes that code underwent can be overwhelming. When there’s a problem, it’s increasingly difficult to hop into the assembly line and diagnose the issue and often there’s not an precise fix.