Performance Max and the transparency problem

Performance Max can perform genuinely well. It can also absorb a budget and return a number without telling you where the number came from, which is a real problem when the number stops being good.

Both things are true and the tension is worth managing deliberately.

What you actually give up

Channel-level attribution. Spend across search, shopping, display, YouTube, Gmail and discovery is reported in aggregate. You cannot easily tell whether your result came from high-intent search or cheap display impressions.

Placement control. Limited exclusions, and limited visibility into where impressions occurred.

Search term detail. Better than at launch, still substantially less than a search campaign gives you.

The ability to explain a change. When performance shifts, the diagnostic surface is thin. This is the one that hurts in a client meeting.

The cannibalisation question

Performance Max is eligible to serve on queries your search campaigns also target, and the interaction is not symmetrical. In general, a search campaign with an exact match keyword takes precedence — but "in general" is carrying weight, and the practical effect is that a Performance Max campaign can absorb branded search traffic that would have converted anyway at a fraction of the cost.

That produces an excellent-looking result made mostly of demand you already had.

The check: exclude your brand terms from Performance Max — using brand exclusions, or a negative keyword list where available — and watch what happens to its reported performance. If it collapses, you have learned something important.

Making it accountable

Run it against a real incrementality question, not a target. The useful question is not "did it hit target CPA" but "did total conversions rise by more than the spend".

Feed it good assets and a clean product feed. More than most campaign types, its output quality is bounded by input quality.

Keep a search campaign for the terms you understand. Not out of nostalgia — because those are the terms where you want control and evidence.

Segment reporting by asset group. Thin, but it is the only structural handle you get.

The honest position

Performance Max is a reasonable tool with a reporting deficit. If your account cannot survive a month where you cannot explain the result, do not run the majority of your budget through it.