I mean, say you have a certain amount of natural resources (land, chemicals, organisms) and you want to maximise health; or you have a certain standard of health and want to minimise resources used.

To put it another way, I think if across the whole of society we had more small-scale gardening that would be a benefit to human health and the environment compared to exclusively using large scale farming.

Conversely, if the goal is maximum financial profit, or absolute quantity of produce, it is more 'efficient' - i.e. more quantity of your goal for less quantity of your cost - to do large scale farming.