probably imacs and a renderfarm.. or a macpro and a renderfarm.
regardless, it's highly unlikely they're rendering an animation for a commercial on a desktop computer.. they do all the work on one but render it elsewhere
If you've ever been inside of a posthouse or VFX facility you will see rows of Linux or Windows workstation usually made by HP or Supermicro derivatives. This is where the heavy lifting is done with Maya, 3Dmax, Nuke etc. Scenes are animated, lighting setup, simulations run and shots composited before being sent the farm. Regardless of the farm you need heavy duty local machines to push around massive data sets, simulations etc before the sequence is sent to the farm for execution. In most facilities the average machine is a dual 8 or 10 core Xeon with a heavy duty GPU, SSD storage and the fastest network connection they can afford.
Flame bays are mostly HP z840 running Linux
Digital intermediate bays for color timing (Resolve etc) are maxed out HP z840 or bigger machines running Linux.
You will see Mac Pros in edit bays, although they are being replaced by Windows boxes. Almost no professionals in TV or film cut with FCPX anyways. It's all Premiere and Avid. You may see an assistant editor with an iMac handling ingestion.
The Mac still is very popular in audio production, but the lack of PCI cards in the trashcan is something of a problem.
What you will see is website and web content creators sitting on an iMac running After Effects and the rest of the creative suite. This is probably the biggest area still dominated by the Mac.
I have yet to see anyone but an art director making a sketch use an iPad Pro to create anything of consequence..
Some places use the iPad to collect lunch orders or check in at reception.
MacBook Air and Macbook Pros are used by production people i.e. producers, coordinators etc. You rarely see production people run anything but a Mac laptop.
You will see a VFX or 2d/3d supervisor with a MacBook Pro, although a lot of them are switching to laptop workstations running 4-core Xeon by companies like HP, Blade, Dell etc.
All of this is backed up by a render farm that can range form a few to hundreds or thousands of blades running Linux and in a few cases Windows for specific applications.
For a while you saw farms based on the Mac Mini for Creative Suite people, but that's an exception to the rule. But even those are disappearing since Apple killed the 4-core i7 Mac Mini.
The ugly truth is that with a few exceptions you never saw a lot of Macs outside of editorial in production. They never offered the price performance ratio or raw power of a PC running Linux or Windows.
But the Mac did rule editorial, audio, graphic design and web design. Unfortunately this is also changing due to Apple not keeping their hardware up to date or offering heavy duty hardware options.
