A big benefit of the standing calf raise is that it forces your calves to stabilize you with a heavy load on your shoulders. Which improves your calves ability doing their main job - balancing your body as you move.
The calves has two major muscles: the gastrocnemius and the soleus. A standing calf raise will train both of them, with an emphasis on the gastrocnemius, which is the outer and bigger calf muscle. so, you will get both thickness overall and definition in the heads of the muscle.
Balance is crucial with standing calf raises. Due to the fact that the calves can often handle a heavy amount of weight, it is highly important to remain focused and balanced to prevent injury.