Components don't really need to fetch anything, they don't need to be smart. It's up to you where data fetching happens. If you look at fasthx for example, you'll see that routes/views normally handle your business logic and fasthx does the rendering (now with Jinja or htmy). With Jinja for example, it can only work like this. With htmy, you have more flexibility (which can be an advantage but of course it can also be misused).

Async components can be handy for example when you need to load files. See the Snippet utility and the markdown support in the lib. https://volfpeter.github.io/htmy/examples/markdown/