So if you want use cases, you can look it up on the net. And if you want something to bash on, you won't get it from me.
Energy cost can be very low when using Proof of Stake. For example a 7000 transactions per second network could run on the energy of a single windmill: https://www.reddit.com/r/nanocurrency/comments/7ucw1a/the_en...
And for use cases, the second hand car industry is ready for disruption. You could say all blockchain use cases can be also handled by a central database. But this has failed miserably in the car industry. There are plenty of companies trying to log metadata, and as a result none of them have the complete picture. Even data aggregator companies are not able to properly bundle it.
Blockchain could offer a very good trustless solution, where you could log a cars history, and a second hand buyer could consult it.
Therefore, big names are entering this space, and I'm confident we will see blockchain solutions in that market soon.
This is only 1 example: https://www.ledgerinsights.com/mercedes-benz-blockchain-used...
The DHL website also has a nice explanation on their use cases https://www.dhl.com/global-en/home/insights-and-innovation/i...