Annotations are nice way to overlay contents on top of visualizaitons. It can also be a great way to create infographics and easier to place labels on landing pages, dashboards or reports. Add calculated values or ${labels} on annotations.
Here is a workaround of that to illustrate the concept:
https://spotfired.blogspot.com/2018/06/overlay-spotfire-controls-values-over.html
One of our customers also wants the ability to use custom expression to calculate values in annotation.