The segmenting of customers by demographics and psychographics has become an important way to minimize marketing waste. But as Professor David Corkindale points out, you can't segment customers who have no meaningful differences. When I was at Ogilvy & Mather, we assumed customers had a set of 'preferred brands' or a 'repertoire', and that actual purchase behavior could be influenced by availability, temporary pricing, even who one is shopping with that day. So the next time you're looking at creating separate messages for different audiences, run a test to make sure it really drives a profitable difference in response.
Wall Street Journal: Mistakes Marketers Make, 2008-Oct-20, by David Corkindale
That is, the profiles of those who buy different brands usually aren't very different, especially in what are called repertoire markets, where consumers typically buy several brands regularly -- a repertoire -- rather than just a single brand.
Most frequently purchased consumer goods are in repertoire markets, though many consumers don't realize it.