I guess if you’re going to leave your phone where any Tom, Dick, Harry and their nosey children can gawp at it unsupervised then having lock screen notification previews active might be a problem. It would never occur to me to leave my phone unsupervised like that. If I was going to see a colleague in another office per your example, I’d take it with me, that’s basic security, just like not leaving free access to a desk/laptop if I’m leaving the room, or likely to be distracted in a situation where some nosey git might try and have a look at it. There’s screen curtain if you want to leave your phone face up next to you without anything being visible.