It's hardly used, around 300MiB at present, probably things like the mail daemon. It's been useful to have a very slow node, which I can SSH into (after 10 minutes) and kill a chosen process, rather than a dead/OOMed node. But I think the difference is marginal, and perhaps 512MiB would have been a more appropriate size for the partition.

(Swappiness is set to 1.)