Answer:

Affinity targeting is attractive because it’s based off of interest, so the good news is that only people actually interested in your topic are shown your ads. The bad news is that if you set up an account with placement on specific topics, Google will charge extra to show your ads on those topics. Brand awareness can come from any targeting method on Google AdWords or Facebook Ads, but affinity targeting may result in higher click-through rates than other methods–because highly engaged people are more likely to click on content they’re already interested in. Affinity audiences outside the realm of “content” may work for some companies’ brand awareness campaigns as well, such as a retail company that sells furniture and wishes to reach out specifically to Home and Garden bloggers and Twitter accounts. Depending on your business, these people may be just as interested in hearing from you as the rest of the world will be.

You can also use affinity audiences to reach a specific audience based off email signups or website visitors–just use the same format for interest-based targeting (look at Figure 3 above). But keep in mind that most companies don’t start with an affinity audience; they look for them after their ads have already proven successful with other ad types.