When should an ArcGIS user change the reference scale of an existing map annotation?

Changing the reference scale of an existing map annotation is essential when the user brings data into the map that has a projected coordinate system. This action ensures that the annotation, which generally includes text and labels for features, is accurately represented in relation to the scale and projection of the data being displayed.

When introducing new geographic data that uses a different projected coordinate system, the reference scale allows for appropriate scaling of annotation features. If the reference scale remains unchanged while the data's projection differs, the annotations may not align correctly or might become disproportionate, leading to potential misinterpretation of the map's context.

In contrast, other scenarios, such as adding a scale bar, creating a new feature class, or using a map template for different geographic areas, do not necessitate changing the reference scale specifically. These actions might involve other adjustments in the layout or data management but do not inherently affect the relationship between the map's scale and the existing annotations.