But they still have a wall - it's just takes a bit more to hit it. In Linux systems swap is usually 2x memory. With swap set like that, all swap does is raise the wall to 3 times what it previously was.

But for a lot of systems your service will fail shortly after you start swapping anyway, because the performance cost of swapping is so high that it often starts a death spiral (can't handle enough requests, so they start piling up, eating even more memory, until your system dies or you hit connection limits etc.).

So "best case" in a typical configuration is that the wall is a bit higher. Worst case you gain nothing at all from the swap.

Personally I treat it as a failure if we ever hit swap - it means connection limits etc. has been set too high.