How are the setPackageWeight() and getPackageWeight() methods of the \Magento\Shipping\Model\Shipment\Request class used?

setPackageWeight()

1. \Magento\Shipping\Model\Shipping::collectCarrierRates()

2. \Magento\Shipping\Model\Shipping::collectRatesByAddress()

getPackageWeight()

It is used by the shipping modules.

DHL

Fedex

UPS

USPS