If you have had the same drain cleared more than once, jetting is usually what finally puts an end to it.
The difference between clearing and cleaning
A cable makes a hole through a blockage so the water runs again. Everything coating the pipe walls is still there, which is why the problem returns sooner each time. Jetting washes the pipe properly, so the gap between visits gets longer rather than shorter.
Why older West Ashley pipe needs it
Cast iron drains here have decades of buildup narrowing them. Kitchen lines in particular collect cooking grease that hardens as it cools. Both respond far better to being washed out than poked through.
Useful after root cutting
Once roots have been cut out of a line, jetting clears the fine material left behind that would otherwise catch the next thing to come along.
When we will say no
Very old cast iron or clay that has already thinned may not stand up to the pressure. That is exactly why we look with a camera first. On a fragile line we will recommend lining instead, because jetting it could turn a blocked pipe into a broken one.