Ideally you have swap, so that stuff that's not actually in use ends up in swap instead of occupying physical memory.
That's why you still usually see machines with unreasonable amounts of GB of RAM having swap partitions: Instead of having data that's rarely, if ever, used occupy precious DRAM, it's much better to have that data in swap so that the DRAM can contain, say, filesystem caches.
That's why you still usually see machines with unreasonable amounts of GB of RAM having swap partitions: Instead of having data that's rarely, if ever, used occupy precious DRAM, it's much better to have that data in swap so that the DRAM can contain, say, filesystem caches.