Typically, when allocating storage space, you must assign resources based upon theoretical future use. The likely result is that either too much or too little is assigned. If too much, the value of the storage device is wasted. If too little, inevitably, time and money must be spent to correct the situation.
With Storage Virtualization, you can create a configuration which will only physically allocate space as it is actually required. This can reduce wasted storage by upwards of 80%.