I'm all for using tools that don't make bad things easy, but I think threeseed is saying that for hacks and spikes, the "later point" you're referring to might not matter. (I agree that those are the only jobs I'd use Mongo for, too.)
Of course, if you're at a company where those spikes find a way of turning into production code, then it's a different story.
Realistically, though, almost always at least some portion of your hacks makes it into production. And if you're saving 10 minutes for 5 hours lost, then even at a going-into-production-rate of 10%, it's still not worth it.
Hacks that remain hacks in 100% of the cases, are rare :)
I've always thought it would be a great idea to create an explicit "prototyping database" that has limitations that actually prevent you from putting it in production, no matter how small your use-case. Things like "erases random rows after 24 hours" or "default row limit of 100; can increment this by 100 once per day by solving a CAPTCHA."
Of course, if you're at a company where those spikes find a way of turning into production code, then it's a different story.