Not an expert as well, but I’ll share my experience. Used to work for a company that contracted with multiple shipping companies mainly for large palletized freight shipments (FedEx, R&L), but not all of them (UPS, other local freight). We had a business contract with FedEx so our shipping rate for both parcel and freight was ~50-60% cheaper than their standard rate if you were to try to schedule/ship something yourself as an individual, but we still used UPS time to time if a client needed it overnight and the FedEx truck already made it’s stop for the day. For example, FedEx website would quote ~$1400 to pickup and ship a pallet shipment standard from your residential address (this would include lift-gate truck service), whereas it would cost our company $450 because they have a regular freight truck that stops by our company twice a day. Of course we ship out much higher volume, so that’s where FedEx would set their discount pricing to ensure they profit in the end over a long duration.
If a pallet needed to go somewhere overnight, that price can easily double or quadruple depending if it was domestic or overseas, but nothing much changes from my end other than changing the shipping label type.
With our FedEx contract, we also had a regional manager contact for support if issues occurred with the shipment that had much quicker response time than going through their standard support routes.