Update on 2021-08-03: My views remain the same regarding the privacy issues and JS on websites, and I still keep myself away from JS-heavy proprietary Web apps. However, I've stopped supporting the idea that all the JS on the Web should be under some libre license like GNU GPL. Having second thoughts.
- You no longer have to worry about tracking scripts, adware and other kinds of malware. Although there are addons to prevent such elements, they cannot detect all of them, especially the new and yet-to-be-blacklisted ones.
- When you are using a lightweight browser like dillo or a text-based console browser like w3m or lynx.
- When the script is under a proprietary license.