i.e., instead of showing ads more and more when their click-through rate goes up. They show the ads more and more as the ROI (return on investment) goes up.
the ROI is determined by dividing the aggregate conversion value for that ad by the cost of running those ads
so $1000 in total sales to users who clicked a given ad that cost $200 in total to run (for those same users) would be:
1000 / 200 = 5.0
where another ad that you also spent $200 on but only resulted in $600 in conversions would be…
600/200 = 3.0
so the ROI is $5 (income) per $1 of ads in the first case and $3 per $1 spent on ads in the second case.
If you enable that feature, the first ad would be run much more than the second one, in order to maximize ROI of the ad spending