That's correct: spot instances are ideal for batch workloads with relatively little persistent state. If your deadline for completing a unit of work isn't extremely short, and you're already distributing jobs across a pool of worker nodes, it's relatively straightforward to dynamically start spot instances if they're available, and on-demand instances otherwise.

Technically, you're gambling a bit because whenever a spot instance is terminated, you probably need to spend a bit extra to redo whatever work it was in the middle of. But spot instances have such a huge discount that it's almost always worth taking that risk, as long as you don't mind the extra management complexity.