I've taken over AWS and Azure accounts before that were paying tens of thousands for unattached disks, load balancers, big servers that were doing very little that could have just been on a burstable VM. Massive messes that in some cases took months to clean up. So, I can believe there could be a massive bit of cost savings available if it were poorly managed. I've never seen the scale of a company like Twitter, but I really doubt there isn't some dead weight. I know storage is a massive cost, and he has stated he was going to purge accounts that were unused over a certain time frame.