You actually do need to present consistently slow evaluation times when handling encrypted values, as failing fast gives out information that can be used for cracking. But other than that, there usually isn't a good reason to do it.
The more consequential the thing, the more likely that it will still be consequential after some time passes at a human scale, and the more important it is to take the time and be sure it’s done right.
It takes time to catch mistakes-whether mistakes on the operator’s part or mistakes on the system designer’s part-that unforeseen circumstances or malicious actors might be turning to unexpected effect.
In the author’s example of a cryptocurrency heist: had this happened in a US bank, where somebody tried to initiate a $90,000 transfer from the victim’s account to a strange one, there’s a much better chance that, in the days it takes to settle, a bank employee would ask questions or the friend would notice a large pending transaction and question it in time to cancel it.
I mean for that matter, we have examples of fast-settling systems (like credit card fraud detection) where that prudent degree of friction comes from having an automatic system auto-deny the transfer in the minority of cases it finds suspicious, requiring the friend to meet a higher bar of scrutiny for that specific high-consequence action.
In the case of most all $90,000 transfers to strangers in a person’s life, the money’s just as good “day after tomorrow” as it is “just as soon as this block makes it on the chain.” The house/car/rucksack of contraband will still be there, and your money will still be good.
Consider that in a world where almost everything is automated and reacts quickly, some faulty logic somewhere could cascade and lead to a lot of bad stuff happening before anyone even has a chance to notice. Introducing some latency, need for validation, etc, at the right places could mitigate this. I don't think just sprinkling slowness everywhere is the idea.
I do think that the efficiency hype has made us all a little speed blind. It's not like faster = secure either...
But secure implies slower. Therefore, fast as possible implies not secure.