Google's black-box campaign type: you hand it your product feed, creative assets and a conversion goal, and its AI runs ads across Search, Shopping, Display, YouTube, Gmail and Discover simultaneously. Powerful at scale, but it needs data density to learn and it marks its own homework. Two traps. It bids on your brand terms by default, cannibalising traffic you would have won anyway and claiming the credit - add brand negative keywords at account level. And launching it cold, before you have conversion volume and strong assets, hands Google's algorithm a blank map and a full budget.
Benchmark. Launch only with 30-50+ conversions a month, a clean feed and real video assets. Average PMax ROAS is ~2.57x (it blends cheaper broad inventory). Cannibalisation test: pause it for two weeks - if revenue barely moves, it was harvesting demand, not adding it.