Why do we need a Theory-Of-Everything (TOE)? On the heels of some of the discussion about the recent TOE article by New Scientist, what are the key reasons why we need a TOE?  The obvious immediate response is that a TOE should give us a means of making predictions in quantum gravity, but what else might be motivating the need for a TOE.  Is it economical to continue the search?
If this question passes muster, I request respondents avoid the typical debate surrounding string theory in the popular press.  In that context, I think the appropriate question is whether a TOE should be able to solve its own ground state problem, or can one even formulate a consistent theory that can accomplish that task.
 A: Let me start by answering "Why do we look for a Theory of everything". The answer will partially answer the "need" question.
For each of us, from the time we open our eyes and maybe even before birth a succession of TOE s is vital for consciousness to connect with environment. We form consecutive maps of our observations and use them for predicting the next steps in our living experience. Like a developing numerical solution. Then we discover analogue methods which allow us not only to predict but also to control our environment.
So a TOE search is built in our cognition functions.
Then, as a human race we discovered mathematics that could map the world we observe simply and efficiently. This also gradually enlarged our view of the world, and at each level there were scientist proposing TOEs : from earth fire water air, to phlogiston and ether , geocentrism to heliocentrism, progress was slow  because the mathematics was primitive.
With Newton and Maxwell mathematics was advanced by leagues and the effort for a mathematical TOE took off. Then came thermodynamics.
It took centuries for the application of these elegant proposals to appear useful for the man on the street, though at the time scientists thought they had the TOE.
Then came the expansion of our world view with the quantum mechanics revolution in the beginning  of the 20th century. The man on the street is reaping the benefits of this. It took half a century for transistors to appear . In parallel special and general relativity modified kinematics and gravity.
The mathematical tools that developed in parallel were so powerful that for the first time, I think it was Kaluza-Klein, a unification of gravity and electromagnetism showed that the TOE might be expressed as one unified mathematical form, instead of a collection of axiomatic descriptions of disparate physical systems. And this is the road followed since then.
By the end of the 20th century most of the data that the standard model describes elegantly  by unifying strong weak and electromagnetic forces in one mathematical format, had been gathered. Since then the goal for most theorists is to unify gravity in a TOE. 
I want to stress the huge economic benefits of particle research to technology. The glaring example being this very webpage by which we are communicating with each other.Nevertheless nobody could have foreseen it. Most of the cost in the search for TOE is in the enormous, in size and number of people, experiments necessary to validate a TOE. It is very probable that these benefits will continue as long as there are physicists who will pursue the TOE. The economics will most probably make sense.
Will having a mathematical TOE predict unexpected effects that can be utilized as quantum mechanics generated the computer etc age? It is a gamble, probably yes, going by historical precedent. 
The need is the inherent need of the human race to map predict and hope to control its environment. 
A: The correct answer is probably a subjective one, but if by "need" you mean a basic necessity, something without which we cannot survive without -- then no, we don't need a TOE. If humans never evolved, the world and the rest of the universe would still exist, and we wouldn't need to know the TOE for it to continue doing so.
As for why we want to look for a TOE despite the above, I'd like to point out that discovering bits and pieces of the TOE has helped technology progress significantly. If you went back in time and told a caveman you could stack stones together really really high in a way that they won't fall, he would laugh at you and tell you to pick up your club and hunt for food. Little does he know, though, the principles you apply to make that rock tower can just as easily be applied to constructing shelter, ovens, stoves, and other infrastructure that would give the caveman a better life if he stopped to think about it.
As for if it's economical, that depends on your perspective. If the TOE was discovered, new technologies could come out of it that we wouldn't even be able to dream of right now, and advance countless lives and make them better. You cannot put a price to such a groundbreaking discovery. Obviously, the cost of spending time and money and energy into the TOE will payoff greatly in further years, if it was discovered.
On the other hand, if the TOE is never discovered because the end of time came upon us and we still haven't figured it out, it becomes impossible to say if it was worth it or not. Is it worth it to flap your arms like a bird when you're falling to your death from a skyscraper? Is it worth it trying to swim to the surface of the ocean when you're drowning 100 feet below sea level? Those questions, to me, sound like they're in the same vein if we don't discover a TOE by the end of time: on the one hand, it could save us; on the other, it could have been futile all along. But we'll never know.
Finally, if we were to assume that it isn't economical, then we'd have to consider something that is of a more economical route. Removing the pursuit of the TOE would mean removing much of theoretical physics and stopping the expansion of science, stagnating it. The TOE is at the forefront of science, so it's not hard to accept this. What would all these bright minds be doing, if not research? Maybe they would lead normal lives, maybe they would excel, maybe they would fail; some might go into engineering, others into art or writing -- but the one outcome common to all is that there would be no more new theories, and hence no more foundation for new technologies to be built. There is only so much you can do with Maxwell's equations or Einstein's relativity on a practical sense, eventually you will expand on it from data coming from new science. In the absence of new science, your evolution effectively stops, and the world becomes a place where we just race to see who can come up with the best model for an iPad, but nothing more than that.
So is it economical? I'd say it's a subjective question -- as far as expected value is concerned, you can't determine the probabilities of finding new theories and assign weights to the outcomes of discovering these theories or not -- but as far as I'm concerned, it's not only economical: it's necessary.
I hope this answers your question. Your question didn't seem to be very physically rigorous to me, so I just evaluated the scenes which made sense in my mind and here they are. :)
