Data Mining is an important analytic process designed to explore data. Much like the real-life process of mining diamonds or gold from the earth, the most important task in data mining is to extract non-trivial nuggets from large amounts of data.
Extracting important knowledge from a mass of data can be crucial, sometimes essential, for the next phase in the analysis: the modeling. Many assumptions and hypotheses will be drawn from your models, so it's incredibly important to spend appropriate time "massaging" the data, extracting important information before moving forward with the modeling.