Delivery labels paper type, plain paper or blank rectangular?

When printing delivery labels for an FBA shipment, there is a dropdown menu under ‘paper type’ where you can choose either ‘Plain Paper’ or ‘Blank Rectangular Label’. The first one shows one single label that can be printed, the latter shows two almost identical labels side by side, the only difference being the last number of the big barcode is different for one of the labels.

What’s the difference between these options and which should I be using?

Thanks