Of course there are specific niches, but it's pretty easy to answer in general: 'actual professionals' need some combination of two criteria - capacity and reliability/durability/usability. A device which can handle 'large' loads - be it CPU-bound, memory/storage-bound, or even screen size bound, and can be worked hard for 6-8-10-12 hours per day, 5-6-7 days per week without either the machine or the user breaking.

The point is not a professional using a computer, it's a professional computer user - someone who doesn't just use a computer to do their work, but someone for whom the limits of the computer are the limits of the work they can do.