A year or so ago I applied for life insurance.
I was very surprised to get questions from the underwriters regarding travel I have done a few years before.
The only place they could have known about these travels were through pictures I posted online. This was nothing crazy or dangerous but they looked me up online, and found pictures with titles and realized I traveled a bunch a few years before that.
It was not a big deal and did not affect my rate at the end of the day but it was very interesting to realize how these companies work.
In general if you post something publicly people and companies will treat it as public knowledge.