Green Energy

The simple answer is that by running your batteries properly they do not degrate nearly as fast. However doing that lowers the energy which can be stored in the battery. So consumer electronics do not do that. Also important to say is that even at half the storage capacity they are extremely usefull, so degradation is not as much of a problem.

Battery degradation isn't as much of a concern in these cases. Batteries that are designed for grid backup use a more resilient chemistry which makes them heavier, but also last longer.

Consumer whole home backup batteries advertise the batteries having over 90% capacity after 10 years.

In a grid storage application, 90% of the original capacity is still fine, and as other commenters have pointed out, the batteries are recyclable.

Lithium ion can have over 1000 charge cycles.

Sodium ion which is only really began manufacturing last year is in the thousands of cycles with expected prices to be lower than lithium ion. I'm not an expect by any means but I think that it will replace lithium ion in the grid market.

Both of the batteries can be recycled and reused.

But really to answer in the most fundamental way of what use it is? Well it pays for itself. People are installing these batteries because over the lifetime of the battery they make the owners a profit and that's with lithium ion which really isn't great for grid storage, but it is all we have a scale right now.

@AllonzeeLV @Wanderer
therefore we must think of energy storage beyond lithium. Heat storage pools, lifted water for kinetic energy and so on.