How a Performance Max campaign works
A Performance Max campaign is built neither with keywords nor with placements. You give it assets (text, images, videos, product feeds), a conversion or value goal, and audience signals. The algorithm decides the rest: where to serve, to whom, with which combination.
Audience signals are not targeting: they are starting hints, which the algorithm moves beyond as soon as it finds conversions elsewhere. Likewise, Final URL expansion, on by default, lets it send traffic to pages of your site other than the one you intended.
According to Google's documentation, a Search campaign takes priority over Performance Max when the query matches one of its exact match keywords. For other queries, the two campaigns can end up competing.
The blind spots of Performance Max
Performance Max optimizes the campaign's overall result without volunteering where it was achieved. It can show an excellent ROAS because it captures searches for your brand and visitors who had already been to your site: sales that would have happened anyway.
The opposite risk exists too: part of the budget can go to lower-quality placements, whose results are drowned in the average. A satisfactory average ROAS can hide a channel that brings in nothing.
That is why the ROAS of a Performance Max campaign should be judged against an independent measure (back-office revenue, MER, an incrementality test), not against itself.
The controls that remain
Google has added several controls over successive releases. Brand exclusions stop the campaign from serving on searches for your brand, which lets you measure what it brings beyond the customers you already have. URL exclusions and the Final URL expansion setting limit the pages it sends traffic to.
The search terms report shows the queries that triggered your ads, and negative keywords can be applied at the account or campaign level for Search and Shopping inventory.
The most powerful control remains the goal itself. Performance Max lets you bid higher for new customers, or target only them. A campaign that optimizes an accurate value can be steered; a campaign that optimizes a figure inflated by existing customers ends up paying for sales it already had.
Frequently asked questions
Does Performance Max cannibalize Search campaigns?
It can compete with them. According to Google's documentation, a Search campaign takes priority when the query matches one of its exact match keywords; beyond that, the two campaigns can compete for the same queries, especially searches for your brand.
Should you exclude your brand from Performance Max?
It is often the only way to find out what the campaign really adds. Without an exclusion, part of its results can come from people who were already searching for your brand and would have bought without it. The simplest test is to exclude it and see what remains.
How long should you give Performance Max before judging it?
Long enough to get out of the learning phase, then to cover at least one full conversion cycle, the usual time between the click and the purchase. Judging earlier means evaluating a campaign that is still calibrating its bids.
Is Performance Max right for every account?
It needs a reliable conversion goal and enough volume to learn. On a low-volume account or one with fragile tracking, it optimizes noise, and its lack of transparency makes the problem hard to see.