They are good when you are stress testing your setup. They are bad if you are just trying to browse the damned website

Ok. Well, it does happen. Happened a lot more in the past vs now.

It happens on Mac. It's when you get an infinite spinning beachball. Sometimes called beachball of death, but generally called kernel panic on Unix systems.

Most of the time with Macs it starts happening when you have hardware failure. It happens way more on Windows and Linux because of the much larger range of supported devices and drivers and the varying quality of the drivers for them. Most drivers running in Darwin as made by Apple. It's also the reason Microsoft created a certification program for device drivers for Windows.

They are more rare one current versions of macOS. I’ve been using Mac’s for about 20 years and got them a lot a lot in the early days.