Well, if you are doing direct response advertising, you can mark (with utm source) and measure any kind of performance metric (CPA, average purchase price, whatever you can come up with), and if their clicks are not cost effective, you can stop buying them.

And if you do branding... branding is hard to measure anyway.

Note -- I'm not affiliated with google in any way, I just think their offering makes a lot of sense.

It depends what sort of business you're running.

If you're selling a product that's available nationally and appeals to a reasonably big demographic, you might not care much about targeting.

But if your business only supplies weddings in New York, then impressions/clicks by people who aren't planning a wedding in New York are largely worthless.