What is it?
Reality is that which is not imaginary - it is what we see, hear and feel when our perceptive capabilities are unhampered and we are not subject to self-deception or the deception of others.
Why is it important?
A clear view of reality allows us to move toward our goals with fewer mistakes and less wasted time...it allows us to perform at our greatest capacity. Faulty "maps", directions or understanding of where we really are all hinder efficient navigation.
The same common sense applies to virtually all human undertakings and explains the primary problems in the world today - fraudulent representations, poor perception and stubbornness to accept reality when we correctly perceive it. No one benefits in the long-term from alienation from reality - it often forms the basis for win/lose exchanges and though the "winner" seems to benefit in the short-term, eventually that gain is wiped out.
Many companies seem to believe they can put 10 lbs of excrement into a 5 lb bag if only the people tasked with doing it will work hard enough or long enough at it. Can you see how reality may not permit that to happen?
Reality is somewhat like gravity - do we ignore gravity? Or not recognize gravity? Sometimes - but that does not make it go away, and we disregard it at our own peril.