When you deal with the semi-floating C-clip axle, which is found under virtually all GM 1/2 ton and some late model 3/4 ton trucks, the only thing holding the axle shaft in is that clip. So when the axle breaks, the shaft can spit right out. The full floater puts the load on the housing, not the axle, as well as being the retainer for the hub. So if the axle breaks, the hub and wheel stay on. And if it's got a locking diff, the truck can still be limped home, eliminating a tow bill. It is best to remove the broken shaft peices fist, though, to prevent any further damage.
