It's still trivial to target users where browser="safari".

But with Safari's recent changes you can no longer target users on Safari where "non-empty cart"=true, because that relied on cookies and tracking which are no longer available.

On a per-impression basis advertisers are willing to pay (way, way) more if they know they are reaching someone who has already visited their site and been engaged enough to add-to-cart. There are plenty of other examples but abandoned-cart-retargeting is one of the most obvious ways advertisers can see good ROI on expensive ad impressions.