Highly targeted advertising can produce great results and there was a time where Facebook was basically a money-printing machine for affiliate and ecommerce because it was so good at finding and reaching the perfect customer. This has become saturated and results have dissipated somewhat but it's still very strong.
It's not impossible that Facebook and Google capture all of the value--or more--that their clients generate by running ads: Bob's Burgers runs $500/mo worth of ads, only generates $400 in (new) profit from them, but is afraid to stop because Paul's Pizza is also running ads and they might lose even more marketshare.
They found that paid (i.e., ads) and unpaid traffic were nearly perfect substitutes for brand names: people will either to get to eBay. For non-brands, clicks go down, but sales don’t; ads are mostly attracting “browsers”, rather than buyers.
The real answer is that it probably depends a lot on the industry, market, and individual business.
Otherwise why continue to run the ads? A smaller but profitable marketshare is better than a larger but negative one.
Prediction and attribution are really hard. I linked a paper below showing that eBay was wasting money on entirely ineffective keyword ads. I can’t imagine that most small businesses (especially brick and mortar ones) are much savvier.
Putting up a large sign outside convince store is going to target people in the area well enough. Giant companies like Disney can easily produce different ads to target individual slices of the population for similar results. But, how well can a small river rafting company for example leverage demographics data? Meanwhile because some companies find this data useful they suddenly need to pay a premium, which just doesn’t seem likely to pay off on average.
My personal experience is that it is pretty hard to get consistently good performance running campaigns on FB or Google. It requires a lot of learning and a lot of trial and error. On top of that, they constantly push you to spend more by giving you dubious recommendations on how to “improve” your campaigns. Very hard to believe that the average small business is actually capable of running good campaigns and consistently make money from them.
Keep in mind I'm talking about targeted advertising, not advertising in general.
