I asked this question a couple of weeks ago. It didn't get much public response. However, someone mentioned that there is a possibility of danger especially for women who, in their professional duties, might have occasion to meet strangers in non-public places, e.g. real estate agents.
There are sickos who target by how someone looks so this is something that should be considered. (of course, after consideration, one may decide the advantages outweigh a remote possibility of danger)
If asked, I advise people to not post photos of their children on the web for this reason. Many school districts will not allow photos of students to be displayed on their sites.
For adult clients, I mention the possible danger and let them decide. I think of it as informed decision making.
Sorry to throw water on the parade.
Personally, I, too, like seeing photos of people. But I don't hold it against them if they don't have one. They may just be being cautious.