Hierarchy is a type of control. It disrupt the natural order of things, usually using large quantities of energy to do so, placing the beings that are the object of control in a state of stress, which denies one or more of their needs, products, behaviors, or intrinsic characteristics, so that their usual outcomes accrue to the controllers benefit.

Here I describe hierarchy as a clearly negative thing, I have heard some protest at it being used in a negative way. I would suggest that in those instances it would be better to use words like network, position, scale, or even relationship. Hierarchy is a mis-ordering of relationships in a way that rearranges benefit and stress.
So many questions! How do hierarchies exist in our own lives? There are many hidden in plain sight within our lives, the more we look the more we’ll find. What energy is used to maintain them? Could we use that energy in a higher leverage way? What stress is imposed on the controlled? How does that also affect the controller? What benefit is given to the controller? What happens to the controller if that benefit is removed?
I have been exploring this thought wave over at Glorious Debris. Through this process I am seeing permaculture as a removal of hierarchy.