Designing to fill up empty niches in space and time so we get continuous production from the system as a whole should be the aim of any permaculture design.
The measuring of yield, in all its forms, energy, nutrition, social life and many other forms should be according to what an area produces in total rather than how much of one thing could be produced.
The limits of the yield depends on the imagination of the designer.
These are some great examples of how to obtain a yield from Deep Green Permaculture, Tierra Permaculture and Verge permaculture followed by Geoff Lawton’s animated versions of the Permaculture Designer’s Manual figures 2.3 and 2.4 on the difference between how an industrial system produces an egg and what the permaculture way of producing an egg is. But first enjoy this song by the Formidable Vegetable !