How some businesses use Expedited/Time-Based Services:
Deliveries to warehouses that require shipments to arrive on a specific day or the shipper is assessed charge back fees against the cost of goods invoice.
Just-in-time manufacturers that need supplies to be delivered for line work on a specific day within a specific hour to meet "production line" requirements.
Your shipment is already in transit. Your customer calls and needs the shipment two days earlier than originally specified.
You need to have your shipment to the port to meet the next sailing date to Europe, Asia, South America, etc.
Freight meeting up with an installation crew.
Your customer wants to stock their shelves with your merchandise before the store opens to the public.