Hydrogen has the highest level of energy by mass of any fuel, but as the lightest element it is also, in its natural state, extremely low in energy by volume. It is therefore necessary to store hydrogen at a high density in order to make it viable as a fuel for transport and other applications.
Hydrogen is an energy storage medium. Energy, stored as hydrogen in the form of a gas or a liquid, will never dissipate until it is used, making it a good application for emergency generators and other mission critical energy applications. Compare that to other energy storage types like batteries and capacitors which lose the energy stored in them over time and need to be periodically recharged even without use.