I also want to highlight the advantage of IOLib based sockets.
The underlying socket API provided by most of the OSes today is the same - BSD sockets. Various Lisp implementations multiply this basic API by proving their own, distinct lisp versions of socket APIs. On top of it we create a compatibility layer, to unify the API.
OSes: 1 API "BSD sockets" => Lisp impls: 10 APIs => usocket 1 API.
If we use some FFI library like IOLib to access OS socket APIs we avoid all these redundant 10 intermediate APIs.
Best regards, - Anton