> Can you elaborate? I haven't run into any roadblocks yet but I'm not scraping big sites or sending a massive number of requests.

Cloudflare Bot Protection[1] is a popular one. The website is guarded by a layer of code that needs to be executed before continuing. Normal browsers will follow through. It can be hard to bypass.

[1]: https://www.cloudflare.com/pg-lp/bot-mitigation-fight-mode/