@Giana
No, nothing to do with Peanut Butter I'm afraid :-D

Cycles:
A render engine developed (I believe) mainly for Blender and allows you to render using your CPU (or GPU for a massive performance increase).

CPU:
Stands for Central Processing Unit, and is the processor you have on your motherboard.

GPU:
Stands for Graphics Processing Unit, and is the processor you have on your graphics card.

PBR:
Stands for Physically Based Rendering, and is a system where all the materials interact in the scene as they do in real life.

To handle PBR in a usable manner requires speed and efficient math, and this demands increased processing power.  So, for example, where a CPU might have only 4 or 8 cores to do the processing, a GPU can have hundreds of cores, and this is why rendering on the GPU as opposed to the CPU, is such a big deal.  The performance advantage is masssive.

The complaints aren't over the choice of renderer (Cycles), it's that they've not implemented GPU rendering even though Cycles does GPU rendering.  The choice to use Cycles was a very good one, but the choice to deny GPU rendering was a bad one, because it does it, and does it extrelmely well indeed.  Cycles was a much better choice than DAZ made with iRay, there is nothing as sure as that, but GPU rendering is a big deal.  I suppose in the worst case scenario that even with only CPU rendering it will be much more interactive, and that's good, but it will be nothing like the interaction speed you get when it runs on a GPU.  With GPU rendering, I can rotate a scene in Cycles and it's that fast it's rendering the scene as I rotate it.  And just seconds after I take my finger off the mouse, the scene is rendered.

All of that, and I only have two quite old GTX 460 cards in my system.