In short: optimised targeting is ticked by default on Display and authorises Google to spend outside your audience — hence that 70 % of spend on people you didn't choose. In PMax the same idea is called a signal. Switch it off for remarketing, small accounts and tight budgets; leave it on only for prospecting with solid measurement, and watch placements daily.
You pick an audience, launch the Display campaign… and two weeks later the report shows that 70% of the spend went to people who were not in your audience. It is not a bug: it is optimized targeting, a box ticked by default that authorises Google to widen your audience. This lesson explains what it does, how it relates to the "signals" in automated campaigns, and how to decide.
What does optimised targeting do?
In Display campaigns (and in video with certain settings), with the box ticked Google looks for people outside your audiences that it believes have a similar likelihood of converting, using your audiences as a starting point and your conversions as the goal. In practice: your targeting becomes a suggestion, and Google buys reach wherever it thinks it will convert.
When it works: with clean measurement, conversion volume and a budget that is not limited — the algorithm has something to learn from and room to explore. When it doesn't: small accounts, soft conversions (Google will find people "similar" to whoever clicks «show phone number»), remarketing (you don't want to widen a list of abandoned baskets to strangers).
What are signals in PMax and Demand Gen?
In Performance Max there is no targeting: the audiences you add are signals — hints about where to start — and Google always goes further. In Demand Gen there is real targeting (your audiences) with an expansion option (optimized targeting) similar to Display's. The full spectrum:
| Campaign | Your audience is… | Can you keep it to your audience? |
|---|---|---|
| Search | Observation or Targeting | Yes |
| Display (optimized targeting off) | Strict targeting | Yes |
| Display (optimized targeting on) | Starting point | No: it expands |
| Demand Gen (no expansion) | Targeting | Yes |
| Demand Gen (with optimized targeting) | Starting point | No |
| PMax | Signal | No, never |
When should you switch off audience expansion?
Switch it off (strict targeting):
- Remarketing (all its variants).
- Campaigns with high-intent custom audiences that you want to measure cleanly.
- Accounts with < 30 Display conversions a month, or with soft conversions.
- Limited budget: the expansion will eat it.
Leave it on (or turn it on):
- Awareness/prospecting with solid measurement, a comfortable budget and an appetite to scale beyond what you can define yourself.
- When a controlled test (below) shows that the expansion converts at an acceptable CPA.
How do you measure whether the expansion works?
In the audience report Google shows rows for your segments plus a row for "Expansion" or "Optimized targeting" with its own spend and conversions. The direct comparison (CPA of your audiences vs CPA of the expansion) is the first data point; the second is an experiment with the box on/off in two copies of the campaign over 4 weeks. Judge by conversions per click and by total lift: expansion on Display is the land of dubious view-through conversions and dubious placements (next lesson).
Which mistakes are made with expansion?
- Not knowing it is on (it is, by default).
- Turning it on in remarketing and "discovering" that remarketing is no longer remarketing.
- Judging it by view-through conversions.
- Leaving it on in a small-budget campaign and wondering why the chosen audience barely gets any impressions.
💡 Ninja trick: expansion is the door junk placements walk in through on Display: while looking for "similar" people, Google buys cheap impressions wherever they are, and where they are is farms and filler apps. If you leave it on, placement monitoring stops being weekly and becomes daily — which is exactly what Ninja Shield does.
What you should remember
- Optimized targeting (Display, on by default) widens your audience; in PMax everything is a signal; Demand Gen has its own optional expansion.
- Switch it off in remarketing, small accounts, soft conversions and limited budgets.
- Leave it on in prospecting with solid measurement and budget; measure it with the expansion row and an experiment.
- Expansion on = placements monitored daily.