Cable assembly is synonymous with "Wire Harness", "Cable Harness", "Wiring Loom", and "Wiring Assembly". A cable assembly is a collection of wires that are held together by various methods.
Cable assembly is very important for the maintenance and longevity of anything that uses electric wiring. Inside a vehicle, for example, there are hundreds of wires that each serve an important purpose. Everything from the brake lights to the instrument panel is connected to the battery and generator via wiring. If there is a break or short in any of those wires, you can lose function. To protect the wires from vibration and the elements, they are clad together in a protective sleeve. This not only protects the wires, but also makes them easier to maintain, as well as install.
The usual candidates for cable assembly are automobiles, air/spacecraft, anything computer-related, and anything that uses electricity and is susceptible to weathering or cross talk. There are many forms of cable assembly. The type that is used is generally determined by the manufacturers' needs. For instance, an automobile or spacecraft would need more stringent and weather-proofed cabling than say, a cellular phone. A computer with thin wires at a low voltage would use a different assembly than a power substations' thick and high-voltage cables. Typically the different types of assembly are for the areas of rigidity, ease of access, weathering and volume. A person who is tidying their home entertainment center would likely use adjustable Velcro straps or zip-ties to keep their wiring in order. Computer-related assembly would use a lot of crimped terminals due to the number of wires contacting a small space. A car might use a plastic sheath harness to protect the wires from sharp edges and heat. A spacecraft would likely use a flexible and highly durable harness.