Classic View
A common approach in modern economics is to divide the economy in the primary, secondary, and tertiary sectors. The primary sector extracts resources, the secondary sector transforms those resources into goods, and the tertiary sector provides services in and around those goods.
Though this perspective can help understand how any specific object came to be, that resources are required before an object can be manufactured and served, it cannot describe the relative value of these objects and services.
Necessary, Useful, and Superfluous View
A more descriptive approach is to divide human activity into necessary, useful and superfluous sectors.
The necessary economy we can understand as all activity that is required for society to live in the short term.
The useful economy we can understand as activity that though not completely necessary in the short term either renders necessary activity more efficient or helps humanity to adapt in the long term.
The superfluous economy is that activity which serves no purpose.
Though there may some areas were there is wide disagreement on what is necessary, what is useful and what is superfluous, which we will touch on below, most people would agree that water, food, shelter are necessary things, that some tools, some crafts, some knowledge and all some art are useful, and that over-consumption is superfluous.
The disagreement is of course on what tools, what craft what knowledge and what art is useful and what exactly we can consider over-consumption or other superfluous activity. For instance, I consider hand tools useful and large infrastructure superfluous, I consider knowledge about how to coexist with the ecosystems we depend on necessary and knowledge about how to control these ecosystems in the short term superfluous (unless used to manage the damage we have already done, or to offer further proof that such a strategy cannot possibly work in the long term), etc.
But regardless of whether one agrees with these statements or not, it cannot be avoided that activity can be necessary, or useful, or superfluous, as categories exist independently from what exactly, if anything, is in them, and from these abstract view certain other abstractions can be deduced.
Firstly, since the necessary economy is essential for the life of society, when hard times society will make every effort to support this activity, and next useful activity, and lastly try to limit superfluous activity to concentrate effort and material where it is necessary or useful. And so, those that find themselves in the necessary economy have far greater security when society faces serious problems; and so, whatever one’s opinion of what activity is indeed necessary or useful for society, one should either work directly in these fields or have the ability to work in these fields quickly.
For instance, currently I am writing this book, which I believe is useful but not necessary, so if some crisis occurs which obliges society to focus on only what is necessary I may find it difficult finding some necessary task to do and so support from society to do it, if I concentrated solely on this writing work. However, aware of this, I choose to live in the country and I learn organic gardening and maintain relations with the organic farmers of the area, so that in the event of a disruption to the status quo I may integrate quickly and smoothly into the necessary economy.
In the event of a minor crisis, which requires society to refocus on only that which is necessary but can still spare material and effort to support what is useful, regardless of my belief that my writing work is useful, society may disagree. So, not only do I maintain the ability to integrate into organic, hopefully tree, agriculture, I also strive to diversify into plenty of other useful skills, such as solar concentration design and construction, welding, mathematics, Linux, programming and website creation, editing, dish washing, translating, cutting wood by hand saw and axe, political philosophy, tiling and whatever else I have learned (some well and some less well) in hopes that in difficult times for either society as a whole or only for myself one or more of these skills will be recognized as a contribution to society (and hopefully actually be a one); or failing any recognition of worth, these skills would allow me to live as independently as possible. Which is of course another way to say that increased comparative autonomy and diversity increases stability.
Macro Economic Disruption
In a macro economic perspective, we can note that the necessary economy supports the existence of the useful and superfluous economy, regardless of the mechanism. [1]
Clearly, too many people doing superfluous things, and more importantly with experience only in such things, is very dangerous for society as in the event of a crisis, the failure of the necessary economic system due to natural or human causes, there might not be enough people in society who can do necessary things to support society as a whole.
However, a superfluous heavy society we should also expect to be unstable even while the necessary economy functions. For, though we may argue about what is and is not part of the necessary economy, physical reality provides a constant test and proof so that society has learned things such as air, water, food and shelter are of the utmost necessity, and all other things less useful to one degree or another. When we arrive at things that, though may be considered to useful by some, are highly debatable and clearly not necessary such activity is vulnerable to be no longer supported by society due to a mere change of opinion, and not any real physical change such as a drought, soil erosion, or peak oil. And so by whatever mechanism the necessary economy supports the superfluous economy, in the event of a change in opinion a section of the superfluous economy may collapse. In the event one section of the superfluous economy is required to justify the existence of other superfluous parts this superfluous collapse may be cascading.
This instability decreases when the majority of people in what may be a superfluous activity have ways of integrating into what is more clearly necessary or useful activity. But we can note that this is difficult in a highly urban society as cities provide nothing of what is necessary and there is a limit to what is useful.