Coil springs are part of your strut style suspension that tend to crack and break sections off that can end up digging into the sidewall of your tires or even falling out and send spring steel cartwheeling down the highway.
Leaf spring suspensions also have a tendency to crack a leaf once in a while and partially go missing at the side of the road.
At every service, your suspension and driveline components are inspected to provide you with up to date information on pending future services.