The cable serves as a way of connecting computers and machines that are far apart. If you have a compact build where all components touch each other (directly or indirectly, most blocks also behave the same way as cables) you will usually not need cables.
Cables can be colored using any kind of dye. Colored cables will only connect to cables of the same color and to light gray colored cables - the default color. This can be useful for running cables for multiple subnetworks in parallel, without using covers.
If necessary, cables can be covered using Forge MultiPart covers, or Immibis Microblocks covers. Keep in mind that 3D prints are Forge MultiPart compatible, so it is possible to print custom covers, if desired.