Why the need: One way to better a model a transistor is to tweak parameters under circuit simulator environment, save the model file and re-run the simulations over and over. The process is painful, time-consuming and error prone.
More efficient method is to use commercially available tools like Agilent ICCAP, Silvaco UTMOST, but unfortunately I had no access to such tools when I needed those the most. :)
Part of my thesis work involved SPICE modeling of the device we were proposing, and unavailability of such tools was almost like a road-block then. I worked around the problem by developing similar software tool on my own by acquiring necessary proficiency in mathematica in less than three days!