In short, class struggle determines the distribution of income between classes (As Proudhon put it, the expression "the relations of profits to wages" means "the war between labour and capital." [System of Economical Contradictions, p. 130]). This, in turn, is dependent on the balance of power within any given economy at any given time.
In a nutshell, a lot. While economists like to portray their discipline as "scientific" and "value free", the reality is very different. It is, in fact, very far from a science and hardly "value free." Instead it is, to a large degree, deeply ideological and its conclusions almost always (by a strange co-incidence) what the wealthy, landlords, bosses and managers of capital want to hear. The words of Kropotkin still ring true today:
Within capitalism, economics plays an important ideological role. Economics has been used to construct a theory from which exploitation and oppression are excluded, by definition. We will attempt here to explain why capitalism is deeply exploitative. Elsewhere, in section B, we have indicated why capitalism is oppressive and will not repeat ourselves here.
C.1.1 Is economics really value free?
C.1.2 Is economics a science?
C.1.3 Can you have an economics based on individualism?
C.1.4 What is wrong with equilibrium analysis?
For anarchists, class analysis is an important means of understanding the world and what is going on in it. While recognition of the fact that classes actually exist is less prevalent now than it once was, this does not mean that classes have ceased to exist. Quite the contrary. As we’ll see, it means only that the ruling class has been more successful than before in obscuring the existence of class.
Private property is in many ways like a private form of state. The owner determines what goes on within the area he or she "owns," and therefore exercises a monopoly of power over it. When power is exercised over one’s self, it is a source of freedom, but under capitalism it is a source of coercive authority. As Bob Black points out in The Abolition of Work: