For as long as Performance Max has existed, the deal has been the same: hand the algorithm your assets, your audience signals, your conversion data, and trust it to find the best mix of Search, YouTube, Display, Discover, Gmail and Maps on your behalf. You could nudge it. You couldn't argue with it.
That's starting to change. Google is now alpha-testing a channel-level adjustment inside PMax — sliders that let you tell the system you rate one channel's conversions more than another, or less. Push a channel up and PMax will tolerate a higher cost per acquisition to win more of its volume. Push it down and PMax tightens the screws, and that channel quietly shrinks.
Eighteen years of watching Google roll out "advertiser control" features has taught me to read the fine print before I get excited. This one's worth getting a bit excited about — but only if you use it with your eyes open.
Why this actually matters
PMax's biggest complaint from day one has been the black box. You could see spend go up on YouTube, watch conversions attributed to Display, and have precisely no lever to say "less of that, more of this" — beyond starving the whole campaign of budget and hoping. Google's own documentation has been blunt about it: no direct channel-level budget control, full stop.
This isn't quite that — it's not a fixed percentage split, it's an economic nudge, letting the algorithm accept worse-looking numbers from a channel you value and demand better ones from a channel you don't. But it's the first real crack in "just trust the machine," and for accounts where PMax has been quietly overweighting a channel that doesn't suit the business, that crack is useful.
Where it'll go wrong
Here's the bit that worries me. The obvious move, the first time this rolls out properly, will be for people to open their channel report, see YouTube's directly-attributed cost per conversion looking expensive next to Search, and yank the YouTube dial down. Job done, tidier report.
Except a chunk of PMax's YouTube spend was never meant to close the sale on its own. It's doing top-of-funnel work — putting the brand in front of someone who later searches your name and converts through Search, getting all the attribution credit for a journey YouTube started. Tighten YouTube because its last-click number looks weak, and you can quietly starve the very channel that was feeding your best-performing one.
That's not a hypothetical. It's the exact trap last-click thinking has been setting for advertisers since long before PMax existed — this control just gives you a much faster way to fall into it.
Before you touch a single slider
- Look at assisted conversions, not just last-click, before judging a channel. If a channel you're about to tighten shows up heavily in assist paths, you're not looking at its real contribution — you're looking at a fraction of it.
- Change one channel at a time. PMax's channels don't operate in isolation from each other. Move two dials in the same test window and you won't know which change did what.
- Give it real time before judging the result. A channel adjustment reshuffles where the algorithm hunts for conversions — that takes the system days to settle, not hours.
- Decide what you're actually optimising for first. If you don't know whether a lead from YouTube is worth the same as a lead from Search to your business, you've got no basis for deciding which way to push the dial anyway.
The point
More control is a good thing. I've wanted this lever for years. But a lever is only as good as the hand on it — and the accounts that get hurt by this feature won't be the ones that ignore it, they'll be the ones that use it to chase a tidier-looking report without asking what each channel was actually doing for the business in the first place.
Same rule as ever: know what a customer's worth to you before you let anyone — human or algorithm — decide where to spend to get one.
Russell Anson runs Compulsion, an independent paid-search consultancy. Eighteen years in, pointed at the only metric that matters. compulsion.agency