Basically, if you cut spark completely or cut fuel completely (or both), there is no firing in that cylinder. That's technically a misfire. Although in my experience a misfire is usually described as a cylinder not firing when you want it to (instead of deliberately causing it). You can save fuel by not injecting any into a number of cylinders under low/no load conditions. However, it is difficult to counteract the vibrations associated with stopping cylinders from firing.