There could be a theory that by drying them in the pods, they wreak out the last of whatever 'goodness' they've acquired during the season, so by taking them out before drying them, they 'might lose' that little extra.
I used to leave all sorts of beans in their pods until Mrs Growster decided that she wanted to pod the lot as they were getting in the way, and took up too much room...
Our 'problem' with growing them at home now, is that we really don't have enough room for more than 30 or so plants, (even The Sutton Dwarf), and what with some of them not coming up to scratch, we never have enough for seed next year as, like today, they're going in the saucepan!