A call-to-action is something we are all familiar with and see in almost every form of advertising. But when it comes to writing copy for PPC ads, it's not used nearly as much. The value of including a call-to-action is in communicating exactly what you want users to do when they get to your landing page, thus improving the chances of conversions, increasing ROI and meeting your campaign goals.
This is much easier said than done since Google limits you to 25 characters in the ad headline and 70 characters for the body (35 per line). Even good copywriters struggle to fit everything they want to say into these restraints, so deciding to replace parts of a working ad with a generic call-to-action takes some finessing.
The idea of eating up 19 characters for the phrase "Sign Up Now to Save" could be a tough one to agree with when additional, informative text about the product or service could fill that space. But isn't that what you created the landing page for? To be that final influence for the visitor, complete with all the information needed? Relying on your optimized landing page and using the call-to-action is advantageous in most situations because it tells the visitor exactly what action is needed and guides them to the next step of the buying process.
When writing a call-to-action, you should aim for the visitor to complete those actions you are measuring as conversions. This could include a final sale, newsletter sign-up, e-mail request or a download. For example, a call-to-action that reads "Contact Us Today" should not be used when watching the demo on the landing page is counted as a conversion. "Watch a Demo Now" or "See How it Works" would be more suitable.
A call-to-action is not always appropriate or necessary, but it does help motivate visitors to move beyond the ad and take the suggested action, which will increase your campaign ROI. Try split-testing different ad copy, some with call-to-actions and some without, and see what appeals to your audience most and then adapt accordingly.