I don't really understand what problem you're solving by doing it that way.

Instead of storing data (let's call them samples) to durable storage to begin with, you're letting the OS write them to swap which incurs the same cost, but then you need to read them from swap and write them to a different partition again (~triple the original cost).

Actually the VMM is pretty performant, all things considered. Having more memory, managed for the process by the VMM, means less fuss doing a flush than if you were to memory-constrain things out of the gate.

Yes, sometimes, it's perfectly acceptable to flush to disk because you're getting low on RAM. But, on systems with, say .. 4x more swap than physical RAM .. you don't have to do a flush that often - if at all. This is great, for example with high quality audio loads that have to be captured safely over long periods.

A system with low RAM and high swap is also a bit more economical, at scale, when building actual hardware in large numbers. So exploiting swap in that circumstance can also effect the BOM costs.