Your client who sells sports shoes might choose to target a custom affinity audience if he wants to:
- reach men, women and children of all ages who need any kind of athletic shoes
- sell high-end running shoes to competitive marathon runners
- increase brand awareness
- reach shoppers who are ready to buy right away
Explanation: With custom affinity audiences, advertisers can create audiences that are more tailored to their brands, compared to our broad, TV-like affinity audiences. For example, rather than reaching Sports Fans, a running shoe company may want to reach Avid Marathon Runners instead.
Read more here: https://support.google.com/adwords/answer/2497941?hl=en