We take the analysis of all our media campaigns pretty seriously around here. When a small or medium sized business needs web ads, we make sure to hit the exact target customer. We purchase web ads from multiple exchanges and through several methodologies to ensure maximum delivery and constantly check the market pricing.
That doesn’t mean we always do it with a laser. Sometimes it really IS better to broadcast to the entire population, especially if there are future customers there you don’t need to reach right now.
Depending on your audience size, it can be a mistake to over-target a specific customer. It’s true for all media, but especially the web.