Quote from MasterAtWork:
Yes it's widely used in practice, specially for computer implementations.
Like series with functions, discret fourier transforms provide a quick way to reach convergence for series approximations on derivatives pricing.
Basically, fourier transforms provide a way to transform time into frequency for signal analysis.
In finance, it's a way to transform a partial differential equation into an ordinary diffrential equation with stochastic calculus to price very quickly derivatives.