I don't want to give too much details but my company allow you to subscribe to people's PTO calendar. By default, you can see your teammates but you can search other people and add their calendar to your dashboard.
To me it seemed like a logical thing to do to add all those people who I interact with to my dashboard. Also I added some of my friends and some higher ups. Just to help me with planning my vacations and sure a bit of curiosity.
Now I wonder if my company can use this against me.