Mostly by the cost? As for sets, they’re going to be 200+ easy.
Theres also some difference in tolerances, but to be honest, a super tight tolerance is a double edged sword. Bulk-produced bolts won’t be as tight anyhow.
For casual/infrequent uses, it’s totally fine to get the inexpensive ones. (I’d recommend going to a local hardware store, they tend to have not totally-shitty sets and most sizes/threads individually.)
Also, for printed parts, you can absolutely just cut in with the bolt, unless your printer is somewhat inconsistent, a with a well-calibrated printer, all you really need to know is how much your holes tend to shrink (the thermal contraction as the plastic causes the final diameter to be smaller. This is why we invented test prints…… well. Not me. Somebody’s smarter than me.)
So there’s zero need to directly connect the pc to the printer. Usually there’s either a microsd or similar to plug in and load to print from that.
However, if you want to, Pronterface is a useful tool for providing command inputs via usb.
It gives you a basic gui to set temperature, manually move the print bead, some telemetry (real time temp charts,) and if you really felt like it… you can print small files across the usb (or push them to the sd and tell it to print from there. Though file transfer rate is usually dog-breath slow.)
Most usefully, it has a command line interface that allows you to send manual gcodes. This is very helpful for tuning and maintenance. (For example m851 will report XYZ offset, and you can set it with for example m851 z-2.47)
Or if you use UBL, create and store the g29 meshes (and if you add t to the command it’ll report values. For example g29 l0 t will load the mesh in slot 0, and report in the box.)
There’s a ton of useful g and m codes.