A cable drills or pushes a path through whatever is in its way, and the pipe reopens to roughly the width of the cable head. That is often enough for one isolated clog. Grease, soap film and years of buildup coating the inside of the pipe are a different problem: a cable punches through the middle of that coating and leaves most of it stuck to the wall, ready to narrow the line again within weeks. A jetting hose sprays water outward in every direction as it travels the pipe, stripping that coating off the full diameter rather than tunneling past it.
It is not the default first step for every clog. A single blockage with no history of repeating usually just needs a cable, and we will say so. Before recommending jetting, a camera confirms what the pipe is made of and how much wear it already carries, and pressure gets set from that, not guessed at.