It's not really about OCD but about physical strain. I like desktop keyboards with numpads, but for a few months I had to use a laptop with a numpad.... and it's horrible from ergonomics viewpoint, as either I'm sitting to the side of my screen leaning asymmetrically to the right or I have the screen in the proper position for my neck but my hands are curled in an inappropriate position towards the left.

It's not a big thing, but doing so for (say) 10 hours every day adds up and screws up my back. If a keyboard has a numpad, then it must be "movable" separately from the screen.