In terms of what people should, or shouldn't, be telling the world about their activities, I remember the days when people living outside the wire were encouraged not to tell their neighbours what they did for a living, because of the IRA threat.
Contrast that to today, and the particular example of LinkedIn. The number of senior officers, both recently retired and still serving, who include in their experience in their LinkedIn profile their current and previous jobs titles, such as:
Director of special weapons development.
Director of investigation of recovered UFO technology.
etc
etc
Ok, I made those jobs up (or got lucky?), but hopefully you get the point. Want to know who to coerce, blackmail, threaten or honeytrap, to get information in specific areas of interest. Just google LinkedIn and a few buzz words relevant to your topic and you'll find your man... or woman!