well in my particular example it's a juicebar she frequents when she's had a bad day. So, she probably lives or works in the neighborhood. And a detail I didn't share was that she was attractive (her icon on the map was her headshot). So someone could get it in their head to approach the person and know what she looks like, where she might be, and believe she needs cheering up

And it's NYC which has all sorts of people, many of which you may not want to be approached by.

If the juicebar gets tagged, then the people working there may start interacting with the friend in a way she may not appreciate.

Sending out life specifics, even if your not famous or have a stalker can be detrimental. And, it wasn't the friend's choice either. So, the original poster may loose a friend in exchange for likes on X.

The thing that never makes sense about this threat model is she lives or works in this neighborhood, which in NYC is many thousands of people. They see her, they can approach her, they can follow her back to her apartment if they chose. To get to said juice bar, she’s likely walked past a dozen mentally ill homeless people and maybe ridden the subway, where you’re confined to a metal tube underground with NYC’s most interesting for minutes at a time.

But none of that registers as a risk: instead it’s a hypothetical X user who is so struck by a headshot on a map that they travel across the city on the off chance she’s still at the juice bar? That’s like worrying about being struck by a meteorite, but paying no attention to the risk of getting hit by a car.

If a friend is posting a person's location, they likely post other information about that person. The aggregate information could allow the assembly of a much more complete picture of a person than is possible by observing a person at a random juice bar.

For example: are they married? Do they live alone? Who are some of their friends? Where do they work? What do they do at work? Have they recently lost/found/experienced something interesting? These are the kinds of details that can enable social engineering in digital and physical spaces. It's likely easier to lure a person into a dangerous situation if you reference minute details from their personal life.

Sometimes the threat model is "has $10k in a bank account" or "is young & attractive" or "practices a religion I don't like" or "it's Tuesday."

It's not their data to share.

Perhaps they didn't tell their friend about that one abusive ex or an affair their having. Additionally in this case it is telling people that when this person is in a certain location they are having a bad day, possibly opening them up to harassment a scam or manipulation.

There are a lot of people that will use that information to their advantage, even if it is just for trolling.

For me, if I found out about a post like this I would stop any contact with the person effective immediately after informing them of not appreciating the post.

I can't relate to this perspective (which seems very common and growing) that there is no intrinsic value to privacy. It's a nothing-to-hide-nothing-to-fear mentality. 'The New Openness' as Trevor Goodchild would say.