At the very fundamental level, there are only two things that can be done with money*. (*Hayek Austrian definition of 'money') You can spend it, OR You can save it Spending is easy enough; exchange money for goods and services. Saving is accumulating to facilitate spending at a future point in time. Its a valid rational option to expend your spending power when the prospects of it diminishing makes continued accumulation a form irrational of behavior. (There are those who call investing the third option, but its debatable since it has characteristics of both.)
And consumption is just another step towards the heat death of the universe when thermodynamic equilibrium is reached and maximum entropy finally erases all trace of our brief existence.