TRANSFERFIELDS function

Hi,

I'm using this function to do following:
I have 2 tables with same field IDs and data types but destionation table doesnt have 1 field that the source table has (it's a field from primary key in source table). I read the help file about this function. It says the following:
"...If the InitPrimaryKeyFields parameter is set to false, the TRANSFERFIELDS function will not change the timestamp or the Primary Key fields of the destination record.
If the InitPrimaryKeyFields parameter is set to true, and the records are in the same table, the TRANSFERFIELDS function will change both the timestamp and the Primary Key fields of the destination record.
If the InitPrimaryKeyFields parameter is set to true, and the records are not in the same table, the TRANSFERFIELDS function will change the Primary Key fields of the destination record (if the fields fulfill the conditions specified above) but the timestamp of the destination record will not be changed."

The default value of the parameter InitPrimaryKeyFields is TRUE. My case is displayed in red.My question is: What is timestamp? WHat does it mean that it will change the Primary Key fields of the destination record (because for example posting from Sales Header to Sales Shipment Header uses Transferfields without optional parameter and it seems to me it doesnt change the Primary Key fields)?