Author said almost always. Nothing is absolute in cases like this. I agree with the article. We enable swap on our production servers precisely because the engineers don't rectify their memory leaks or whatever problems are internal to their software. Some of those engineers are our own and we can't convince them to fix their software. Others are for things we have no control over, such as Kafka, for example. When Kafka starts going out of control and you've got no swap, oom killer will kill it and you'll end up with corrupted index files, which is a bigger problem than the performance problem you'll see if it has to swap for a while until it gets itself sorted out.