I've been running ads for 15 years. At my previous job in ecommerce, I managed a six-figure monthly Google Shopping budget. I'd looked at every dashboard, pulled every report. I could tell you our ROAS, our CPC, our conversion rate by category. I could even see, product by product, where the impressions were going. But knowing and controlling are two different things.
Products I knew mattered were getting almost no impressions. Products nobody on the commercial team cared about were eating massive budget. I could see it happening. I just couldn't do anything about it.
That problem hasn't gone away. If anything, it's gotten worse as PMax has become the default. And the data backs it up.
The Budget Distribution Problem Nobody Audits
Most retailers don't know their PMax budget distribution because the data is there, but it doesn't tell you anything useful on its own.
You can pull a report with thousands of product rows. You can see impressions, clicks, cost per SKU. But what you can't see is how that spend maps to what actually matters to your business. Which strategic categories are getting budget? Which ones aren't? Is your new product launch getting visibility, or is all the money going to last season's bestsellers?
Most teams never ask those questions. They see overall account performance, maybe performance by campaign or product group, and assume the algorithm is doing its job.
Here's what happens when you actually look.
Your product catalog doesn't get equal attention. Not close.
What the Data Says
Big Flare ran an audit across their retail customers and found that 59% of products get zero impressions in a typical quarter. Zero. Not low impressions. Zero.
JumpFly found that 54% of products in audited accounts are what they call "zombie products": visible in your catalog but functionally invisible in your ads.
Peter Plesko reported numbers that put 70–95% of products outside the visible set on any given day, depending on how you define visibility.
The pattern is consistent across every audit: a small fraction of your catalog gets most of your money. The rest gets almost nothing.
And this isn't a bug. It's how PMax is designed to work.
Why PMax Concentrates Budget
Performance Max is a machine learning system. It's incredibly good at one thing: finding the products and audiences that convert most efficiently right now.
If one product converts twice as efficiently as another, the algorithm learns fast. It starts shifting budget toward the higher-converting product and away from the lower one. This is the system working correctly.
The problem is that this optimization happens without context. You can dig into the data and see the result, but there's no warning when 60% of budget drifts toward 20% of products. Nobody asks whether that's actually what your business needs.
The algorithm has no idea that your “low ROAS” products are:
- Your strategic priorities for the season
- Products that build customer lifetime value
- New product launches that need visibility to grow
- Categories that define your brand
To PMax, a low-ROAS product is a low-ROAS product. The algorithm will minimize investment in it.
This is optimization without context. And over the course of a quarter, your budget quietly drifts away from your strategy. We call this budget drift: the gap between where your money goes and where your business actually needs it.
The Business Cost of Blind Allocation
Let’s get specific about what this costs.
Say you’re spending €100k per month on PMax with a few thousand products. If 59% of those products get zero impressions (which is what the audits show), more than half your catalog is getting nothing. Zero visibility. Zero chance to convert.
Your entire budget goes to the rest, maybe 40% of your catalog. The algorithm picked the winners for you. And the products it ignored? Some of those are your strategic priorities, your new launches, your high-margin categories. They’re in the catalog. They’re just not in the game.
One of Expanly’s customers ran this audit recently. They found that 40% of their budget was going to products they wanted to run down. Legacy SKUs that needed to move. Meanwhile, their hero products (new category, premium margins, strategic growth driver) were barely getting budget. When they reallocated, ad-driven revenue from those hero products tripled in two months. Different budget allocation. Same ad platform.
This is what budget drift looks like in practice. You’re not wasting money. You’re spending it efficiently on whatever the algorithm decided matters, which may have nothing to do with what your business actually needs.
From Visibility to Control
The first step is seeing it. You need a clear picture of how your budget is actually distributed across your catalog, segmented by what matters to your business: margins, strategic priority, category, new vs legacy.
If your strategic products are systematically under-funded, that’s budget drift. The algorithm is working correctly. Your strategy and the algorithm are just misaligned. We run this audit for free, and it usually takes less than a week to get you the full picture.
Here’s what changes everything: Teaching the algorithm what matters.
At Expanly, we built this specifically because most retailers either accept the drift or try to fight it manually. That means hours of spreadsheet work, constant campaign restructuring, and changes that break the next time the algorithm re-optimizes.
The cleaner approach is business rules. You define segments that matter to your business. You allocate budget targets to each segment. The system makes sure your budget follows your strategy, not just short-term ROAS.
Once the rules are in place, PMax finally gets the context it needs to optimize against your goals, not just conversion efficiency. Setup is fast, and the rules update automatically as your strategy changes.
You still get the power of PMax optimization. You just add the control layer on top.