When I design sheet metal electronics boxes, I arrange the box, end panels and mounts so that the bottom sits 6mm above the table. This gives me room to insert PEM nuts. All components and all screws are inserted from above. There is no need to access the bottom of the box. By orienting fasteners correctly, I implement one of the basic rules of DFMA.
When you design machined components, you need to watch where you place machining radii. You can cause extra machine set-ups.
You need a sense of perspective when you do all this, but lots of it is simple, and does not require a lot of thought.
Like I said, DFX etc. does apply to lower volume work, but the trade offs in time spent V benefit etc. are different so 'extreme DFX' that is time consuming or takes multiple iterations may not be appropriate.