You're right that most of the time you don't need to use JavaScript.

But look at Google Groups for example - there is an infinite scroll to get all the topics, posts are also loaded dynamically, so you have to wait some time to get them.

In the SFO flights example you have to deal with pagination also using JavaScript.

We wanted to build a powerful tool which can crawl and scrape almost any website out there. It's slower, but you can use bench of our nodes to do it in parallel.