My computer now is in a tower case. It's tucked into part of the knee hole I'm not occupying. I can reach it on the rare occasion I need to insert a diskette. Otherwise, I just sits there, out of the way, doing its thing. But not in the places you often find them.
Most writing desks are too high for keyboards and too low for monitors.
The monitor should be placed so you are looking straight ahead or slightly down. If you use one of those monitor stands, it's typically too high, causing neck strain. Consider the room lighting. Glaring light bulbs reflect on the monitor screen and make them hard to read. Best are fixtures that diffuse the light or even bounce it off a white ceiling.