Apple also points out that the old Mac Pro had room for four hard drives, two DVD drives and four expansion cards, but those were arbitrary numbers. It was far too much wasted capacity for some people, not enough for others (like video editors who need many terabytes of storage). In response, Apple designed the new Mac Pro to be only the brain, with all of its organs external, so that you can build precisely the system you need.
You might buy those arguments; you might not. And even if you agree with Apple’s assertion that external expansion is the future, you might not like it. It might mean replacing a lot of gear you’ve already invested in, or finding adapters that accommodate their new, external status.
It all boils down to whether you need what the Mac Pro offers: ridiculous horsepower. You can read all about it here, but the point is that every wire, every circuit, every chip has been designed for speed. Intel’s new Xeon processors. Up to 64 gigabytes of memory. Four USB 3.0 jacks. Two gigabit Ethernet jacks (you can connect to two office networks at once). An HDMI jack so you can connect a TV directly (a big deal for video editors).
No SD memory-card slot, though. No traditional spinning hard drive, either. Instead, the main “hard drive” is made of flash memory, of the sort inside MacBook Airs, tablets and phones. Saving files and opening them are ridiculously fast — this flash drive is 10 times faster than most hard drives. But even if you max it out to 1 terabyte ($800 more), that’s not much storage for video editors; again, external storage is going to be part of your future.