I can definitely see the utility in the feature, it's just that it, conceptually, is such a security risk that it's simply not worth it, even ignoring the data harvesting/storage penalty.
You enter a discussion and you need to refer to an article you know you've read but can't find? Now you can find it. You want a backpack and remember seeing one you liked but can't remember where you saw it? Ask it to show backpacks you looked at - great now you've tracked it down in seconds rather than spending half an hour.
But yeah, the security and privacy implications of this are so bad that it's really not worth the tradeoff.