In Platform on a guest time line each receipt will potentially have a different classification depending on how the order was placed.
The "Served By" line shows on a POS receipt, a POS receipt is done at the point of sale in the restaurant. That is why it has a served by line for in the restaurant you could potentially have a server(waiter/waitress).
In comparison a "Mobile" order will not show a "Served By" line on the receipt.