Hi

The origin is set in the firmware. It can be in any corner of the printer or it can be in the center of the heated bed. The simple way to locate the limit switches on the Pegasus was to put them in a way that gives you a back right or upper right origin. There is nothing wrong with doing this and it does not in any way mess up prints.

In any coordinate system the origin is 0,0,0 by definition (or 0,0 if it's a two axis system). The convention usually is that +Z is the "up" direction and X and Y are the left/right front/back axis. If you want your bed to be +X and +Y that gives the rest of it. On most printers the Y axis is the front to back one and the X axis is the left to right. There is no absolute reason why you could not do it a couple of other ways (possibly with negative numbers). It's a bit simpler to just stick with the conventional approach and move on.

Bob