Despite a few recent positive updates, Performance Max continues to suffer from a notorious lack of targeting controls.
While there are limited windows into the PMax black box, peeking through the few that exist reveals generous helpings of the low-grade inventory that Google is eager to monetise however it can.
For example, the PMax campaign placement report (find it under the ‘template gallery’ in the report editor) almost invariably reveals a preponderance of low-quality placements.
(These were the top placements seeing impressions in a PMax-for-Travel campaign – for a high-end resort:)
So it’s natural enough that we should want to take advantage of whatever targeting levers we do have…
Audience signals and search themes are the most recent.
Rather than offering my own opinion on their value, I recommend reviewing Optmyzr’s excellent study from March this year, showing the average ROAS associated with PMax campaigns that do vs don’t use these features:
But when it comes to the use of Search Themes, I do have a couple of pointers on how they can (and how they don’t) add value.
1 No need for 'obvious' search themes
PMax takes its thematic queues from your landing pages (like DSAs), your feed (like good old Shopping Ads), as well as your text lines and images.
Those methods are well established and – ultra-obscure industries aside – they do a good job of determining the product, the theme, and where relevant, the appropriate search terms.
True, we often find PMax veering into unwanted territory, but not because it fails to understand what the ‘right’ territory is.
So doubling up on this with search themes that essentially mirror your product will only duplicate those existing signals.
At best* this is an opportunity cost, repeating signals that are already clear, rather than leveraging search themes for what they’re meant to target: themes not covered by your landing page or other assets.”
As PMax expert Daryl Mander puts it:
The whole purpose of search themes is to target keywords that are not already present in the information you've provided to Google Ads.
For example, let's say Father's Day is approaching, and your product is popular as a Father's Day gift. However, you might not have the phrase "Father's Day gift" on your landing page or in your product titles. This would be an ideal time to instruct the system to target this keyword by adding it as a search theme.
Another scenario is when you've just launched a new product or offer that lacks performance data. In this case, if you don't add a search theme, Google might not bid aggressively enough to test the new offer, as there is no historical data on it. Adding the search theme acts as a way of telling Google, "Here's a new offering; please attract traffic for it.
2 The Trojan Horse
By adding your ‘core terms’ as search themes – you are inviting PMax to encroach on the territory best reserved for your dedicated search campaigns.
Precisely because of the amorphous appearance and mixed quality of PMax inventory, it is generally a good idea to do what we can to keep our ‘core activity’ separate.
Otherwise PMax will dilute the chaff of its low-quality inventory with the wheat of your profitable clicks – and present blended performance data consisting partly of high-quality traffic that would and should have come your way via other campaigns.
You can then leave PMax to work with the ‘outer edges’ of inventory that you are not already serving with greater focus in other campaign types, and judge it accordingly.
If it can produce incremental conversions in that space at an acceptable ROAS/CPA – then it truly adds value.
Recommended actions like trawling your PMax search terms for high-value phrases to then add as exact-match keywords, and excluding your brand from PMax, to serve brand terms instead via search and shopping, are in tune with that general principle.
Search themes for core terms go squarely against it.
A recent update to Google’s keyword prioritisation rules now places Search Themes high in the ad serving hierarchy.
When a search term exactly matches a search theme, the associated PMax campaign competes on a level playing field even with search campaigns that have an exactly-matching phrase-match keyword. Only an exactly-matching exact match keyword definitively trumps it.
So while adding search terms for your product and other core terms may seem intuitive, it damages any attempt to limit the ‘PMax creep’ that sees it pinching value from other campaign types to present itself in a misleadingly positive light.
