If you’ve ever set up a machine by hand, you’ve probably had to decide how much of your disk to set aside as swap.
I’ve often wondered “why swap at all”? This quote by Nick Piggin from 2004 finally helped me answer the question.
no matter how much ram you have, swap can increase performance by allowing unused anonymous memory to be paged out, thereby increasing your maximum effective RAM
Found via this post on Hacker News, where the poster raises the point that some filesystem buffers might be extremely “hot” (frequently used), but might only fit in physical RAM (where they should be) if some swap space is available to page out other “cold” information.
Update 2016-12-22: except for Kubernetes nodes, apparently.