Performance Max (PMax) campaigns are Google’s automated advertising campaigns that use assets such as a product feed, ad texts, images and videos.
Where Performance Max ads are shown
Performance Max ads appear across Google’s various networks and platforms, such as YouTube, the Google Display Network, Gmail, Google Maps and — of course — Google search.
The advertiser, however, has no control over how the advertising budget is allocated between these networks. The automation decides, guided by the campaign’s conversion goal — so as to maximize its achievement.
Conversions in Performance Max campaigns are reported mainly based on clicks, but in some cases they may also be reported after an impression (e.g. conversions after watching a video). This means conversions across different networks may not be comparable.
Information about how impressions and clicks split between the networks isn’t reported directly. Partial information can be gleaned from reports such as the placement impressions report, asset reports, the report broken down by Merchant Center IDs, and the reports inside Merchant Center itself.
Network allocation data in a digestible form can be obtained with scripts, e.g. from Mike Rhodes:

A Performance Max campaign without assets (feed-only)
PMax campaigns can sometimes shift budget toward display or video ads in an uncontrolled way. For many advertisers, a safer option that gives more control is to use only Shopping ads in Performance Max campaigns.
This is possible if we launch a PMax campaign without adding assets — with the product feed alone.
Google, however, makes creating such campaigns difficult: the Google Ads panel won’t let you save the first asset group unless assets are added to it. So what then?
After creating the first asset group (with the mandatory assets), you can add another group without assets, then pause/delete the first one — done.[stopped working in May 2024]Another way is to create and upload a PMax campaign without assets (feed-only) via Google Ads Editor.[stopped working in May 2024]- Campaigns without assets can be created from within Google Merchant Center.
Changes don’t roll out to all Google Ads accounts at the same time, which means that in your specific case some of the outdated methods may still work.
Google Ads technology is constantly changing. Despite our efforts, some of the information in this article may be out of date. Drop us a line if you notice the text needs updating.
See also the article on negative keywords and audience exclusions in Performance Max campaigns.