I'd be interested to know if if there's a tangible impact in doing this. If so, that would mean it's probably always worth checking if execution can continue immediately before creating a continuation wherever possible – but that often involves checking some synchronized state which comes with a small hit itself.
But this post about UnsafeContinuation says that if a continuation is resumed synchronously within the supplied closure, no suspension takes place at all. Suspension only takes place if the continuation hasn't been resumed synchronously within the supplied closure. That suggests to me there would be no benefit to performing a prior check – and maybe even a performance hit doing the unnecessary work.