Placed within arm's reach, the hardware of your CPU can now be accessed quickly and easily- no more ducking underneath your desk or pulling your tower out. Most CPU holders pivot or rotate at their attachment point- giving you access to the front and back of your computer tower without having to leave your seat. This functionality also makes cable management much easier. Ergonomically, the CPU holder eliminates the need for unpleasant straining just to access the computer tower underneath the desk.
There are lots of reasons to buy a CPU holder, especially when it's made by Humanscale.
Also, because the CPU holder lifts your computer off the floor, it increases ventilation to it- reducing wear and tear and increasing its lifespan.