I have to assume there would be a more than 50% loss through the process, hope someone on hn can comment. Maybe it's not worth it when you can tap into unlimited sunlight the next day.
The density is the problem.
If you raise a 25,000kg mass by 100m, that's 24.5MJ, or roughly the energy contained in one kilogram of coal. Or 6.6kWh (standard meter units) of electricity.
(and that's on the input side, not accounting for losses)
It's an actual implementation of energy storage, the water is pumped up there and then gravity distributes it, so there is a buffer if the pumps can't run for some reason.
Flywheels are also pretty good short term, but supercapacitors mostly do their job better these days. That said they are competitive, and technological changes could nudge them into more use. Just making your wind turbine really large gives a flywheel effect, e.g., so again if you already have a spinning thing they are often worth it.