Here's a more concrete and practical example: If you spend $50k on content marketing and SEO, and another $50k on ads, which is giving you the best bang for you

Here's a more concrete and practical example: If you spend $50k on content marketing and SEO, and another $50k on ads, which is giving you the best bang for your buck? In the current JS-based ad world you can go: my ROI on the first is X with reasonable confidence; and on the second I believe it is Y after discounting for [heaps of ad fraud-related reasons] -- which is not great, but still better than no idea. In a text/image only ad world you'd go: my ROI on the first is X with reasonable confidence; on the second I've absolutely no idea except that the numbers are getting worst by the month because of [heap of ad fraud related reasons]. The main victim here, I should point out in passing, are the websites you're getting your news from. And yes, you're somewhat correct, the company selling ads can't tell you how effective the ads ultimately are. But only they can tell you if the ad likely got served to an actual human rather than to a bot, among other schemes. And knowing that a bot is likely browsing your site can make a world of difference with your boss when you're reporting on whether you should spend more on content/SEO or online ads, or with your payment provider when someone is testing stolen CCs on your SaaS sign-up form.