I have used both - unique SS lines to 4 MAX7219 so each could be individually addressed for updates, and cascading 20 shift registers to drive 12V LEDs. I was going to cascade the MAX7219s, but it got so messy software wise that writing to each uniquely made way more sense. Why write out 8 bytes of data when just 2 are needed for the device at the end of the chain? The tradeoff becomes using more pins & going faster, or using less pins and going slower. I'll take faster anyday.