What we lovingly call 'combines' or 'additional seams' are just that. They are any action taken to a shirt other than the straight cutting of the standard sized square.
Some examples of what is considered extra and does cost extra.
Complex piecing. When more than one seam is involved, or creating a block out of odd shaped items, it requires more time to piece the block.
Minimum of $10 additional charge on these. These can include but are not limited to: