When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
It's when the spring is compressed to the point the coils are touching. At this point you have no more upward suspension travel unless something else bends or breaks.
when they bind theres no room left for the springs to compress therefor maxing them out. coil bind will eventually wear away and weaken the springs. springs are a wear and tear item just like struts.
Many are designed with dead coils. At rest under a car, you'll see some of the coils touching. It keeps them seated when the car unloads going over bumps and stuff. Not a great design though.