Why model in the time domain?
The computer simulation is life-like,
Virtual experiments are set up as in the lab (sources, reference planes, probes, devices),
Cause and effect can be distinguished,
One simulation can cover a wide bandwidth,
Both transient and time-harmonic fields can be viewed as the simulation progresses,
Nonlinear behavior is modeled naturally,
Dispersive materials and boundaries are modeled in a physical manner.