In a Google Ads Help post, Google describes the Optimization Score like this:

"Your optimization score, found on the Recommendations page, helps you understand your account’s optimization potential. The score runs from 0% to 100%, with 100% meaning that your account can perform at its full potential.

"We look across key aspects of your campaigns to evaluate whether they are fully optimized and then offer recommended actions if there is room for improvement. If a recommendation can have more impact on your performance, it’s given more weight on your overall score."

Below is what I found in a trial run on one of our Google Ads campaigns.

First, to get to the Optimization Score, log in to your Google Ads account and click Recommendations in the left navigation pane.

That took me to a screen with this header:

At that level, Google groups its recommendations into 4 categories:

• Bids & budgets (none for me on that one)
• Keywords & Targeting +18.1%
• Ads & Extensions +17.7%
• Repairs +0.1%

Below that comes a series of recommendations, each with Google's estimate of the potential improvement in Optimization Score to be had from implementing it, an explanation of the reasoning behind the recommendation, and a set of very specific recommended changes/additions. Here's just a summary of each of mine:

• Create new ad groups from existing keywords +9.3% Show people more relevant ads by organizing your keywords by theme. Recommended because you can improve your CTR with new ad groups organized by theme.
• Set up audience sources +8% Access remarketing features to increase your ROI by showing more impactful and personalized ads. Recommended because you have enough traffic to benefit from remarketing.
• Add sitelinks to your ads +4.4% Your ads aren't as prominent as they could be if you used sitelinks, which can improve your CTR. Recommended because similar advertisers including booking.com use sitelinks.
• Add new keywords +4.8% Show your ads more often to people searching for what your business offers. Recommended because you're not targeting searches that could be relevant to your business.
• Remove redundant keywords +3.2% Make your account easier to manage by removing redundant keywords. Recommended because you have redundant keywords with the same ad group, destination, bid, bidding strategy and match type.
• Add callouts to your ads +1.8% Your ads aren't as prominent as they could be if you used callouts, which can improve your CTR. Recommended because similar advertisers including booking.com use callouts.
• Upload customer lists +2% Access remarketing features to increase your ROI by showing more impactful and personalized ads. Recommended because you have enough traffic to benefit from remarketing.
• Add structured snippets to your ads +1.8% Your ads aren't as prominent as they could be if you used structured snippets, which can improve your CTR. Recommended because similar advertisers, including booking.com and tripavisor.com, use structured snippets.
• Create new versions of your ads +0.4% Try new versions of your ads and let the best ones show. Recommended because some of your ad groups have fewer than 3 ads and can benefit from new ones.
• Remove non-serving keywords +0.1% Make your account easier to manage by removing nonserving keywords. Recommended because some of your keywords haven't received any traffic for the past year or more.

Sure, like everything else Google creates, this Optimization Score is self-serving because it encourages marketers to use Google Ads (vs. optimizing for organic search, which yields no direct revenue for Google), and is heavy on recommendations that will increase clickthrough rate and thus click charges.

But it also helps us marketers sell stuff, which is what justifies our existence.