What's are the advantages of using the Bill of Material Options, Part Number vs a Custom Property "Part Number"?

We have been using a custom property names Part Number since 2005 and never had an issues with using custom properties.

We have put our files into PDM Pro and will be moving documents from another office into PDM too.  The second office is using the BOM Part Number and Custom property part number on parts but fasteners they only use the BOM Part number.

I would like to understand why SW created the BOM Part Number and if there are any advantages of using it.