When optimizing for the Display Network, a clear call-to-action (CTA) in the ad text is important in order to:
- increase overall impressions for the ad
- identify the traffic to your website that was generated by AdWords ads
- improve the Quality Score of the ad on all Google properties
- set expectations for customers who are in various stages of the buying cycle
Explanation: Be explicit about your call to action, whether a button or somewhere else. This is especially important for image-based ads, because customers may not know what part of the ad is clickable. In some cases, if your ad really blends in well on a website, they may not even realise that your ad is an ad! Don’t make them guess.
Read more here: https://support.google.com/partners/answer/1722134?hl=en-GB