What do I still need to regenerate static content in developer mode?

I’ve written this blog post to resolve an issue with symlinks and extensions/themes in Magento (mostly for personal reference). But I’d like to know why it’s required to redeploy static content in development mode. I thought that wasn’t necessary? https://magentowizard.wordpress.com/2020/02/21/path-cannot-be-used-with-directory/

Thanks for any help.