All of the above. Audio, video, 3D. Any pro level design. Even print design.
Having a Mac Pro with lots of storage and big monitors when you're working on a 300 page book with 300GB of photos is much less annoying than poking along with a laptop.
It's not just the speed, it's also the usability. Eg, a comfortable trackball and a nicer keyboard. Sure, you can add those to a laptop, but then you have a kludge.
How is that a kludge? You have to add them to a Mac Pro exactly the same. And you can just stick all of your "desktop" stuff on a USB hub and call it a docking station...
Having a Mac Pro with lots of storage and big monitors when you're working on a 300 page book with 300GB of photos is much less annoying than poking along with a laptop.
It's not just the speed, it's also the usability. Eg, a comfortable trackball and a nicer keyboard. Sure, you can add those to a laptop, but then you have a kludge.