You can get small machines that are light enough to put on a shelf when they are not being used. Of course they don't have the rigidity to work in hard materials of any size, but for very small stuff (say that you can hold in the palm of your hand) they are okay, but they're not a Bridgeport.
That's a factor. Chips and coolant are messy.
Some of us have these "basement" things, for example, a so-called "4,000-square foot house" with two stories might have an *extra* 2,000 square feet (not counted in the square footage by law) for such purposes, minus a wee bit of space for physical plant elements.
Also, I know some folks (retired, generally) with shops that are larger than their houses. Naturally, zoning becomes a factor in such deviant lifestyle choices.
Best regards, Spehro Pefhany