I wasn't advocating for badly written code to run on a whole datacenter. I was just pointing the alternative with the assumption that the code was somewhat healthy and adding one new instance to cover the sub-optimization wasn't a big deal.
Of course, if you have 10k users and it runs on 3 machines, you got a problem which no amount of boxes can solve.
I'm hardly what most environmentalists would call an "environmentalist", but one cost here is the increase in carbon footprint. Of course, to the company the cost/benefit analysis errs on the side of just spinning up more boxes. But from a larger perspective, taking some extra time to make more efficient use of machines could have a drastic impact. Many optimizations don't require months to implement. Many of those are even avoidable with a bit of foresight.
Of course, if you have 10k users and it runs on 3 machines, you got a problem which no amount of boxes can solve.