We also use level change in the event of the autothrottle being unserviceable, or switched off in the case of an engine failure. The reason is the autopilot or flight director will control the speed and you can then vary the rate of climb or descent using thrust. If you use VS with no autothrottle it's harder as you have to monitor the speed much more closely.
During descent once the thrust levers are closed, the autothrottle (if now working) will go into arm mode allowing you to manually re-position the levers so you can add thrust if you want to reduce the rate of descent, a slightly crude vertical speed mode!