Moreover, notice the example they gave there is atom interning, which is a roundtrip on the wire (though you can batch them even in xlib...), and they say "most real applications will see less benefit than this" since that's the worst case - most applications do atom work at startup, not in the main use cycle, which is famously both async and buffered (it used to be a FAQ on xlib tutorials reminding people to run the event loop, and error handling is complicated a bit by it).