The Fourier Transform analysis of time domain signals that consist of discrete frequencies components added together can be amazingly useful if it is specifically the discrete frequency components that we are after, as for example in various types of spectroscopy. In principle any the time domain signal, such as a chart of closing prices for ES, can be reproduced using a sum of transcendental functions. You can then look at the amplitude and frequency of each transcendental component. This comprises what would be called the frequency domain spectrum of the time domain picture,i.e., of the ES closing prices plotted out. But in the case of a futures chart, what exactly does knowing the frequency components and their amplitude tell you? I'm certain Goldman's quants (the financial industry is the largest employer of Ph.D. physicists in the U.S.) long ago transformed the S&P or the ES into its frequency domain. But what did they discover? Apparently not enough to save them without Fed and Treasury help.