Behave
I've lost count of the amount of times I have seen large demographic reports misused to prove an argument.
Demographic info is important and has its place of course — it can group general regions, affluence and age of your customers and can help make key decisions about your business. BUT (a big but!) it doesn't tell me what makes them tick and what they are interested in — to buy, to do, to stay, to eat. If we don't know what interests them then your brand can become irrelevant.
If I spoke about an affluent male who drives and Range Rover, lives in Surrey and has kids are we talking about Ozzy Osbourne or Prince Charles? (Extreme to prove a point but you get me?) I suspect there isn’t much in common in the way they purchase clothes, accessories, IT or relate to their audience.
I earn about the same as my (2 years) younger brother — I know! I seem like the younger one, right??! — We have totally different lives and job roles that neither of us really understand, different taste in food, like different music and appreciate very different films and he probably thinks most things to do with the design world are a waste of space... we couldn’t be farther apart in our desire for a car, a piece of furniture, a restaurant choice or a holiday (we do agree on nice wine though!) Yet we come up under the same dot under a customer research analysis piece.
I'm pro for digging a bit deeper and finding common interest when it comes to designing an experience for a set of users. It's often trickier than it seems to group people.