This assumes you already want to buy the item in question, and advertising just helps you find the best place to buy it, or the best model to get. Consider the other side of the coin. Let's say Facebook shows you products that you don't already want, but based on your age, interests, and past behavior, you have a high likelihood of wanting. The barrage of ads you see convince you to buy that product. In this case, making the advertising more "useful" through better targeting doesn't save you, the consumer, time and money. Just encourages you to buy something you we're perfectly happy without. So is this the kind of advertising you'd like more of? The kind that sells more products for the company, but doesn't help the consumer make the best purchasing decision?
Now I'm not opposed to advertising, and I think advertising can benefit companies and consumers. But we need to start a debate about the usefulness of advertising to separate good advertising from bad. Please pick apart my example above. I'm sure my argument has weaknesses, and I'd love to know what they are.