Use a tag if record groups can start on any line within the area, but they start always in the same position relative to a tag.
Note:
If the record group is defined with a tag, visual configuration will be unable to calculate the correct line of a primary data column when you map it. If you define a record group with a tag, then you will have to manually modify the primary data column definition. More information is provided in the steps under Record Primary Data Mapping.