Now, to some extent I suspect the initial changes last year were probably the worst and further changes will have a smaller effect. However the wider impact of the whole thing is enormous, particularly for smaller advertisers. Like much of the industry Facebook is taking control away from advertisers and increasing the use of ML (they shot themselves in the foot with privacy invasive initiatives and the legislative backfire resulting in having to hide data from advertisers), that’s how they now claim to “attribute” conversions on iOS. However this means that increasingly you need a larger daily budget in order to have enough data to train their algorithms.
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Copy past of my comment on this a few months ago, it is worth reading the whole thread:
As a rough datapoint, I run a consumer targeted e-commerce site. We ran a campaign before Christmas were we were selling a new product that was only marketed on Facebook, we are certain that (almost) all customers found it though that Facebook campaign. Facebook was only able to attribute about 50% of the sales to the ads, it should have been close to 100%. This then meant that Facebooks estimated CPA was effectively double what it actually was. Important to note about 60% of our customers are on an iOS device, which is a little higher than the global average but matches the market segment we are in in the UK. The situation improved after about 4 weeks, I believe Facebook now uses some "AI" to help with attribution on iOS, but it's somewhat difficult to be sure as by then we had other campaigns running. So, this will definitely be effecting marketers decision making process of where to allocate spend. It certainly made us more courteous about spending on Facebook.