Performance Max has become the default campaign type Google pushes new advertisers towards, and it has taken an increasingly large share of budget in accounts that were built around Search and Shopping. The pitch is simple: give Google your assets, your budget, and your conversion goal, and let the algorithm find the best placements across all Google inventory. In practice it is considerably more complicated, and the accounts that do best with it are not the ones that simply turned it on.
PMax combines Search, Shopping, Display, YouTube, Discover, Gmail, and Maps into a single campaign. The algorithm decides how to allocate budget across these in real time, based on its prediction of which placements will produce conversions. You provide asset groups, headlines, descriptions, images, videos, and Google assembles ads from those assets dynamically.
The critical thing to understand is that PMax is heavily influenced by your existing audience signals and conversion history. In a mature account with strong conversion data, PMax has a lot to work with. In a new account or one with thin conversion history, it can behave erratically, spreading budget across placements that are cheap but not effective, and taking a long time to converge.
For ecommerce with a product feed and a solid history of Shopping conversions, PMax can be a genuine upgrade. It absorbs your Shopping data and extends reach across formats you may not have been running at all. For accounts with high conversion volume, thousands of transactions per month, the algorithm has enough signal to make sensible decisions.
PMax also works well for local businesses using Google's local campaign formats. The combination of Maps, Search, and Display for geographically constrained businesses is a natural fit for the automated format.
Brand cannibalisation is the most common complaint. PMax will serve on branded search terms unless you add brand exclusions, which Google only recently made straightforwardly available. Without those exclusions, PMax appears to be driving conversions that were actually branded searches, existing customers and people who were already going to convert. This inflates PMax ROAS and makes it look like a hero campaign when it is partly just capturing demand that existed independently.
Transparency is the other problem. You cannot see which placements are getting budget. You cannot see which search terms triggered your ads within PMax (only categories). You cannot tell whether your budget is going to YouTube videos that nobody watches or Search queries with genuine intent. If you like to know where your money goes, PMax will frustrate you.
For B2B SaaS with low conversion volume and long sales cycles, PMax often underperforms dedicated Search campaigns. The algorithm needs volume to learn and the conversion events available in most B2B accounts, form fills, trial signups, do not give it enough signal quality to make good decisions quickly.
Add brand exclusions from day one. This is the single most important step to ensure PMax is driving new demand rather than capturing it from branded search.
Use audience signals to steer the algorithm early. Uploading your customer list and adding your best-performing in-market and custom audiences as signals gives PMax a better starting point and shortens the learning period.
Run it alongside dedicated Search campaigns rather than replacing them. Let PMax take the top-of-funnel and incremental placements; keep your highest-intent Search campaigns running independently with clear negative keyword lists to prevent cannibalisation.
Review asset performance regularly. PMax will tell you which asset combinations are performing, use that to update your creative and deprioritise underperformers.
Performance Max is a powerful tool in the right context and a budget sink in the wrong one. It rewards accounts with strong conversion history, good creative assets, and careful setup. It punishes accounts that treat it as a set-and-forget solution. If you want to work through whether it makes sense for your account, I am happy to look at it.