To be clear, I'm not talking about this Mac Pro in particular, but things like the Boxx or Mac Pro.
You would get something like this instead of consumer hardware because man hours cost real money. At a previous job they wanted a VR PC, so someone speced out a bunch of high end parts and a case with flashy lights. A couple days of my salary went to putting it all together. That was the first time I had to RMA a motherboard. When I asked they didn't think to confirm the GPU would fit in the case and luckily it did. It also took a couple weeks longer than it should to get up and running because of things like this.
Some specialty software is only certified for specific hardware. You can probably deviate, but it's like building a hackintosh. You might not be able to upgrade it and the man hours will likely kill any benefit.
I also see a lot of managers forget that artists aren't always tech savvy. Honestly, you don't pay them to be tech support, anyway. You want to pay a known quantity and get improved return. It can be a huge time suck to nickel-and-dime when you're tying to manage large projects.
However, using consumer grade hardware has its place.
Yep and there is a vast middle ground of use-cases. The parent asked about consumer grade hardware versus something like Boxx. I gave 3 separate reasons. A lot of people in this thread are wondering why Hackintoshes aren't an option so I wanted to bring it up.
Honestly, Apple wasn't what I had in mind when I was replying. Personally, I've had to deal with HP z-series workstations compared to various cobbled together machines. Having machines where the series will be in production for a decade, data sheets are readily available, fewer tools needed to open it and install stuff saves so much time and allows less downtime and faster turnaround.
It runs macOS and those consumer grade computers don't. If the best colorist in the area is working on your film, you give them the tools they ask for.
The color graders here run 10-bit/color HDR monitors that have a wide gamut. Apple doesn't have monitors that support this. (The new one _might_ do the trick; we'll see.) Everyone here doing professional color work is on PCs supplied by Thinkmate. This is standard in Hollywood, too.