Comment by rcxdude

I'm sure it's one of the most useful signals for the advertisers, but it is also one of the most irritating behaviours for the consumers, because even if this is a very high correlation in advertising terms, it's still the majority of the time not actually accurate for the consumer (like with all ads: I buy some orders of magnitudes fewer products than I see ads, even with adblocking, so even if I only bought things I had seen ads for, the vast majority are not helpful to me).