Storage is useful for balancing daily load swings when you have sources like fusion, fission or some fossil fuel plants that don't work well off nominal power levels. The pumped storage technique you illustrated is one of the few large scale storage methods which has proved practical and economically useful. But pumped storage, like solar and wind requires some conditions that don't exist everywhere, and don't necessarily scale down to smaller sizes. It is relatively low density energy storage.
1. Significant elevation differences within a relatively small distance.
2. Lots of relatively cheap land for the reservoirs.
3. Lots of available water.
4. The economics work best where the facilities have dual uses (irrigation, flood control, hydroelectric generation of power with water that passes through the system).