When a line has a checkmark in the Split by column, any line in the Calculation with a different value for that property will be given its own line. Any line that has multiple products collapsed within it will have a green arrow to the left. Click on the green arrow to see an expanded list temporarily.
If nothing is checked in the Split by columns, all lines within a group will be collapsed into one, and a green arrow will show to the left of the line:
You will always at least want to have Part Number or Description checked in the Split by column so that any product with a different part number will be on its own line:
In the image above, there are still a few lines collapsed because the lines share the same part number but have different part tags applied. In this case, if you want to see products with the same part number but different tags on separate lines, you will need to check the tag category in the Split by column, in this case TAG1: