At work I was given permission by a vendor to screen scrape their site while they worked on building a real API. This site was extremely dependent on javascript. Including doing some really complex token passing between multiple domains that the company owned. Not to mention all of their js was minified and uglified so I had a very hard time understanding what it was doing.

It was the first time I wasn't able to successfully reverse engineer a site enough to scrape what I needed with just requests/beautifulsoup. I was however able to get it working just fine using phantomjs via selenium via splinter. It was a fun exercise, but part of me still feels like it was cheating.