As a relative layman I also have the same question. If you can turn it off, what makes it so bad?
I’m not saying I trust Google, of course. It just seems like they have a vested interest in screwing over third party advertisers and making them more dependent on Google. If you can then disable the Google part, isn’t it a net benefit?
(I don’t use chrome and am not familiar with this change, so I may be missing something)