This afternoon Hadley Wickham gave a great talk on data analysis. Here’s a paraphrase of something profound he said.
Visualization can surprise you, but it doesn’t scale well.
Modelling scales well, but it can’t surprise you.
Visualization can show you something in your data that you didn’t expect. But some things are hard to see, and visualization is a slow, human process.
Modeling might tell you something slightly unexpected, but your choice of model restricts what you’re going to find once you’ve fit it.
So you iterate. Visualization suggests a model, and then you use your model to factor out some feature of the data. Then you visualize again.