Complex numbers are used for a lot of applications in two dimensional kinematics where rotation is involved. The reason for this is the ease with which a complex number can be differentiated.
That said, I personally never make use of complex numbers for kinematics because I think it ultimately leads to confusion. In a kinematics problem, the quantities involved are invariably real numbers, and it is confusing to have to consider some real number as represented by complex or imaginary numbers while others remain real. It is never necessary. All kinematics problems can be worked entirely in terms of real numbers, and I strongly recommend doing just that. The small extra effort required to deal with rotation is more than compensated by the fact that real quantities remain real.