If you need potatoes but don't feel like growing them yourself, and you like (and/or are better at) painting fences, then exchanging favors (whether or not involving currency) creates value - it's a positive-sum game.
Yes, absolutely! It's the tenet No 1 of a market – when people freely exchange something, both are better off. (No 2: there's some stuff that you can't do without cooperation).
But in the potato-case, all the potato-value and great-fence-you-have-there-value gets added to GDP, where realistically, output only grew by whatever the increase of efficiency was.
Yes, but apart from the women's integration into the workforce scenario, how relevant is this? It doesn't feel like that huge trades happen with "transaction of favor", instead all probably use money.
But in the potato-case, all the potato-value and great-fence-you-have-there-value gets added to GDP, where realistically, output only grew by whatever the increase of efficiency was.