The courier services are optional; you can manage the process on your own.
VFS Global return service is pre-paid, fixed price, 2-day UPS shipping; its return label (pre-paid 2-day UPS) is for the materials to be sent back to you after processing.
The alternative is to create your own UPS account and arrange for shipping, including your return label in the package for when the visa has been process.
As the UK guidance when applying for a visa in the US notes:
To have your documents returned you must provide a fully addressed prepaid electronic shipping label (we cannot accept ground services and non-electronic waybills). Put your return shipping label and envelope inside the package, and keep a copy of the waybill for your records.
As a side note, take care to ensure that the all goes more smoothly, rather than what was experienced by another applicant.