Let's imagine that we have a potential customer database built upon yellow pages, with the customer locations expressed as addresses. I guess that using yellow pages may not be the best idea these days, but it makes a good starting point for this example.
We need to send our sales representatives to these addresses in order to establish relationships with the new customers, but first we should assign the customers to proper sales regions. Having seen St_Intersects in action already, searching for points in polygons seems like a trivial task. We need to have point geoms for this though, and we'll soon see how to go from addresses to geometry using some simple Node.js code.
Let's prepare our hypothetical new customers ...