How we see business owners and their marketing agencies typically evaluate the effectiveness of Google Ads is by evaluating ad spend against how many new clients they procured from ads.
In the AI era, only looking at cost-per-acquisition like this, through one channel at a time, can lead to costly mistakes in one's overall marketing approach. That math no longer reflects how new clients actually find a business.
A new client may have searched on Google or ChatGPT, but they also saw your brand's name offline in everyday life months earlier, recognized you from an Instagram post they scrolled past, or read a review on a third-party website about your business. Later, that user finally clicks on a pay-per-click ad to contact you. The PPC click that closed the deal was real, but it was not the whole story.
The more useful question for business owners to ask is: "What is our global CPA?" (cost-per-acquisition).
Add up the total cost your business spends on marketing, across every channel, divided by the total number of new clients acquired. That number tells you whether your marketing is working as a system. From this basis, you can then look into individual channels like pay-per-click, SEO, AIO, or social media to see which ones are contributing most. Then optimize the individual channels, or shift where the next marketing dollar goes.