People think that adtech has some incredible insights but 99% of data is terrible. If you check your profile at any major site, you'll quickly find that you're probably in several conflicting segments that have nothing to do with you. Context is still king for any marketer who knows what they're doing, but unfortunately the industry is overwhelmed with subpar talent and politics through layers of agencies that buy buzzwords like "AI" and "data". Barely any adtech companies have a direct link to a person, and any links that did exist are even harder now with adblocking, 3rd party cookie deletion, ephemeral mobile device ids, IP renewals, and other noisy and loose signals.
Interestingly, big companies like Facebook and Google that have user logins and 1st party data connections will actually benefit from the higher industry regulation and are not going to lose any of the data that users willingly give to them. ISPs are another major source of data, along with credit agencies and banks, and now giant ecommerce companies like Walmart and Amazon, all of which have very accurate and exhaustive histories and will see little change from GDPR. Overall it's well-intentioned, and good progress, but what it will do is vastly overstated.