I’m curious... if you get the rack version, is it to launch remote jobs for the Mac Pro to run or do you keep the rack near your desk in order to have the display cable reach your monitor? I was recently looking for long TB3 cables but it seems the longest one I can find is 2m. So I don’t see how I could have a Mac Pro in a rack and still have it reach a TB3 display.
In some cases, the rack would be on your desk. A good deal of high-end, custom built workstations (desks) have racks in them, so you can mount hardware and secure them with screws.
A RackMacPro would be off the floor, away from people kicking it or pushing it back and forth, and away from spills. It's a really nice way to keep an office or suite clean and tidy.
In other instances, it's in a machine room that has proper cooling and ventilation, and is easy for technicians to reach. The room doesn't have to be too far from the workstation (in some instances it's on the other side of the wall) and a 2m cable would reach just fine.
If it's further, there'd be a need for an amplifier or to convert the signal into something that is better for longer cable runs, like HDMI or even HD-SDI.
Lastly, like you mention above, and were right on target, some applications will use the Mac Pro for power and remoting in or using a virtual machine would be just fine.
Another way for a post-production house to make it's money (and for Pros to save some) is to rent out suites. So if an editor is renting a Final Cut suite for $XXX.XX an hour you wouldn't want them damaging or taking components from your $53,000 Mac Pro. So mounting and securing it are standard practices.
HDMI and cable runs from machine room into main room
Exactly! Beat me to it.