Frequency domain analysis has much broader application (more numerous to list) than just analyzing sinusoidal components of a signal. Frequency domain analysis appears as a mathematical tool whenever the equivalent operations in the time domain can be simplified, and vice versa. For example, convolution in one domain is multiplication in the other which can simplify many problems. Further given the great efficiency of the FFT to solve the Discrete Fourier Transform, it has found its way into so many applications where the end result can be viewed as simplifying the number of operations needed to solve for a result (such as radar imaging, autofocus, and highly efficient communications). The broader class of the Laplace Transform is also the frequency domain and is used to convert difficult integro-differential equations to simple algebra!