Imagine a courier service that collects and delivers your freight / consignments as per your instruction. The courier collects when you tell them to, they deliver the items at the correct destination at the time you advise them. In this scenario there are no consequences to your business, every goes as planned.
Let's look at another scenario, you book your courier service and they arrive to your warehouse 40 minutes late, there was traffic on the road. Did they inform you? You get the courier loaded, you are now behind on your other deliveries and warehouse staff are being taken off on one job to help the late courier get loaded and on the road. The courier delivers an hour late, your customer has an engineer on standby for the part and has to pay the engineer waiting time.
Another scenario?
Courier arrives on time, loads and goes and that's the last you hear from them. You hear on the radio there's traffic and you hear that there are delays in your customers area and you ring their office and they say they'll get back to you, only they don't. The communication has broken down and you are doing your part, but now you have your customer on the phone wanting to know where their urgent parts are, they should have arrived ages ago...
A good same day courier serviced will save you and your customer's time and money. It takes a little time to sort the wheat from the chaff when it comes to good couriers to use, but you have to know what you are looking for in the first instance to know if they are worth the money.
If an item is to repair equipment or machinery - it's worth the money
If it's important contracts or blueprints - it's worth the money
If it's urgent - it's worth the money
As a business you also have to think about the cost in both money and reputation if you fail to deliver what you have promised. You can blame the courier service, but let's face it, it's not hard to find a great courier service you just need to overcome your reluctance to use one.