I would think common screws and bolts are cheap enough that it would be better to incorporate the real thing into your designs rather than try to print them. I except Ed's repair, because a 3/4-5 is not what I would consider common.
Each machine has its advantages and limitations. Let the lathes handle screws, and the 3D printers, everything else.
General discussion topics
I wouldn't read too much into the question. I tend to explore new things (like 3D printing) by figuring out what the limits of the technology are, then after that comes figuring out what's actual best practice. Lots of possibilities get lost when you ask "what's practical" before "what's possible".