The way I see it, it's basically just a cost-saving measure. If you have some very varying workloads, instead of paying for having a bunch of servers running all the time (and idling most of that time), when you actually need the extra compute power you can let AWS Lambda spin up a server, run the code, then spin it down again. That's clever and all, and might save you a pretty penny if you have huge workloads only part of the time - but for most users, it's hardly worthy of the hype.