Workout role matters in cable machines because the same machine can serve very different jobs in a home gym. For one person it may be the main strength station. For another, it may be an accessory tool used after barbell lifts. It can also support rehabilitation-style work, isolation exercises, core training, or warmups.
Knowing the workout role keeps the purchase realistic. A cable machine is valuable when it fits the part of training the user will repeat most often, not when it promises to replace every other piece of equipment.