Um, you really need to read the entire phrase and not pick out only what you want from it. 😃
Swap can make a system slower to OOM kill, since it provides another, slower source of memory to thrash on in out of memory situations
It means that if you try to use it as a source of memory, when you run out of actual RAM it will make your system almost completely unresponsive due to disk thrash, instead of allowing the kernel to just kill the process that’s eating your RAM. So you’ll just end up hard-booting system.