Funny to see this article—I was interning at a company that used S-expressions instead of JSON internally right around the time this post was written. (Seeing it for the first time now though.)

All I can say is that in practice, s-expressions worked way better than JSON. Easy to read as a human, more flexible than JSON, reasonable syntax for working with alternatives (ie variants or sum types) and, of course, comments.

Here's one thing that stood out to me in particular: you could encode formatted text in a way that was pretty easy to read even without formatting:

(Here is a sentence with (i some words) (b emphasized) in (i (b different)) ways.)

I forget if this was exactly the syntax they supported, but it was something like that. You could do something similar with JSON, but it would be way more verbose and harder to parse visually.

Another massive advantage: structural editing in Emacs with Paredit is incredible. Once you get the hang of it, it's way faster and less prone to typos than "normal" text editing.

If I ever start my own company, I'd definitely be tempted to standardize on S-expressions as our human-readable format for serialization and config data.