Many manufactures do not sell directly to the end user. Between the manufacture and the user is usually a channel of distribution. They are essential to the success in any type of business. If you run a service business you need the supplies used that create the business, in which case you are a channel for the manufacturer or distribution of the supplies.
For instance, an HVAC company needs their air conditioners, heat units and service parts so the technicians can perform their job. The business maintains open channels for these items. Let’s face it, how would you react if the repair person fixing your air conditioner failed to have the proper parts with him or even at his shop?