As someone who teaches PhD students who are quite far beyond "average professional", I concur completely with PG on this one. Writing forces you to make very clear and concrete ideas that feel like they make sense but are still fuzzy. It's certainly not the only way, but it's the most common and easy way.
To use an overextended computer metaphor: serializing data structures to a wire format forces lazy evaluation, turning up any errors that were previously hidden by laziness.
I don't disagree, just want to mention that as someone married to someone who supervises Phd students, they're not by any means "far beyond average professional"... but perhaps you're on a exceptionally highly regarded faculty where that may be the case.
