Can someone please explain in simple terms - what exactly mining computation is used for?
The proof of work is required to prevent block spamming and mitigate the risk of double spends.
I mean, all the firepower used for mining around the world put together - is it all really needed for security purporse?
Sounds like a hell of a lot of machines to me - is it really justified?
There are alternatives, like Proof Of Stake for example.