Apparently the person who wrote that guide had no real idea what that setting did and subsequently should not be giving computer advice like they know what they're talking about.
Mess with that setting and you run the risk of gimping your computer. Don't believe my simple word? Here's what happens when I set that drop-down to use
3 of my 4 cores.
For those who just don't get pictures...
it disabled one of my cores in Windows. That's what the setting does. It and the maximum memory setting next to it are likely for troubleshooting obscure things by
restricting system resources. Certainly not for using more resources than it would normally.