trying to wrap my head around what the difference is between onboard, and external stepper drivers. all my google searching has come up in vain. I assume they have different capabilities. the external stepper drivers i see on ebay and various CNC builds, seem to be bigger in size, than what the Openbuids Blackbox has, or other boards like Duet. does bigger mean better? I know that external and onboard drivers both come in a variety, with different prices, and capabilities. Im just trying to get a sense of why someone would pick one, over the other, for a particular project. 3d prints, CNC mill, laser engraver, etc.