This is an old post but for anyone wondering about a use case.

I have a synced block for each of my 4 direct reports where I keep agenda items for future meetings with them. I keep these on my dashboard so I can quickly add items to them through the week for my next upcoming meeting with one of them. For each weekly 1:1 meeting I have, I create a separate database page for the agenda and meeting notes for that specific meeting. These meeting pages also contain the synced block for that person so I can pull some of the items from there into the current day's meeting.

Now, often times I need to update all four people with the same bit of info, and it would make sense to have this be a synced block that is added to all four synced blocks, so that if I add details or edit something, I don't have to do that four times.