Segmentation is a tricky topic, and the type of segmentation model that you will want to use will depend on what type of action you are trying to convince your target audience to take. I work for a charity, and we try to convince our supporters to donate. We have a very limited amount of resources allocated to fundraising. Most of our revenue goes to our 'real' work, conservation; but none of that could occur without our support team. Additionally, there is a point at which it begins to be more cost effective to not mail unresponsive segments, as it sometimes doesn't raise enough money for the resources invested. So our problem is, with a limited number of letters to send - who should we mail?