I can't believe people are actually wasting energy to calculate stuff that is useless.
You shouldn't believe it because it's not true. Mining secures the network by making it computationally difficult to reverse or alter transactions after the fact, which is extremely useful. I think what Jacce meant was that mining has no use outside the context of the payment network, which is technically true, but misses the point completely.
Yes, that was my point, but I wasn't sure exactly how to say it (not a native english speaker). And you're right that it's good for the coin, but if the coin itself doesn't have any real value then it's pretty much useless because the mining (with a few exceptions) don't do anything useful except helping the coin.