[lwhi]

If you want to replace all the styling in your project, because you've had a rebrand; I would argue that CSS in JS makes your life more difficult.

If you want to share styling between your app and your website; I would also state that this process is made more difficult.

If you want to create, implement and maintain an atomic design system to build in consistency and reuse .. again, more complicated that it might have been.

To add to that, this article suggests that there's a performance deficit.