These cranes have a second boom with articulation near to the middle. This provides some unique performance characteristics.
Lift heavy loads
With a short boom crane, the reach fully retracted is less than a standard crane, and the shorter radius equates to a higher lift capacity. In many cases, a "C" version crane can out perform a larger crane with a standard boom when performing a close lift.
Lift tall or high loads
With a standard boom, positioning it for a close lift will mean that the hook is not very high. This limits the height of objects placed near to the crane. With a "C" version, the second boom is set back, allowing a very tall or high load to be lifted.