This box will automatically be checked if the current row is a setup price row. Setup price rows will be automatically inserted directly after a part row, provided that a setup price is linked to the part.
Setup price rows are handled differently than others regarding statistics. When the statistics are updated, the setup price is saved to the statistics for the above part. However, in the Supplier Invoice Log you will see the setup price specified in a separate column.
You can link several setup price rows to one part, but then the box Setup price row must be checked manually on the manually entered setup price row (this is to make sure that the purchase statistics for the setup price rows are saved for the part).