If you are an advertiser for a product (let's say a fishing) pole and you are targeting a certain demographic (let's say people who might buy a fishing pole) and you know that the person you are targeting, beyond just being interested in fishing pole, is also a family man, you might show an ad that emphasises how fishing is a family act and brings people together. Alternatively if the person you are targeting is a person who likes solitude, you might emphasise the peace and silence of fishing on your own.

That is one reason why knowing your individual target is valuable beyond targeting a certain demographic - you can tailor your ad to the individual, which in theory will increase the likelihood of a sale.