[lern_too_spel]

If you were focused on profitability, you wouldn't run Target CPA. Your marginal cost per action is going to be much higher than the target CPA, making your marginal acquisitions unprofitable, lowering your total profit. That's in the best case, if you have unlimited budget. In the unlimited budget case, Google is at least incentivized to bid on the lowest CPA users first. In the constrained budget setting, they can give you absolute garbage, and it's no skin off their backs. It's even worse if not all of the actions are incremental, which for an established company with unlimited budget is guaranteed.

The past few years, Google has been adding features that make absolutely no economic sense (assuming rational firms), but assuming that most of their clients are unsophisticated and then taking advantage of them has no doubt earned some Google Ads PMs huge bonuses.

[nicklafferty]

Thanks for sharing your thoughts! That hasn't been my experience, target CPA was absolutely the driver of both volume and profitability for that business. You have to know how to work the algorithm and feed it the correct data. I was doing thousands of conversions a day so we had scale in our favor. If you're not careful tCPA can spend a lot of money for sure. YMMV though.

[lern_too_spel]

This is a basic application of the mean value theorem. Moreover, assuming 100% incrementality is what leads marketers to do silly throw money away things like Mailgun bidding on "mailgun" even though all the links on the first page of results are already to pages Mailgun controls.

[ameister14]

Actually, that's not always that silly - if you have a structured campaign that uses ads to send people searching for specific things to the parts of your funnel you have optimized for them you can increase conversions and have a good ROAS even over the same keyword performance organically. It can totally be worth it to do.