Currently the only mandated property when creating a new product / service is the code itself, however I assume other businesses like ourselves require nominal codes to be associated to all products for accounting purposes.
Due to this field not being mandatory, it is having to be applied at the stage where invoices are being processed, rather than at the point of code creation.
I am sure there would be other fields too where some businesses would like to mandate the entry of data rather than leaving as zero / blank.