Try this- move the extruder carriage manually in the Y direction. Now move it in the X direction. Do you feel the extra effort it takes to move it in X? When it moves in X, the belts have to move on two more pulleys than when it moves in the Y direction. Adding extra pulleys increases the load on the motors. That means that if you're trying to print as fast as the machine can go, and you add extra pulleys, you may lose some speed because motor torque falls as speed increases. If you don't care about maximizing speed, it probably doesn't matter.
The most important thing, regardless of the number of pulleys, is to position all the working segments of the belts parallel to their respective guide rails. Working segments are all those that vary in length as the carriage moves. You can do whatever you want with the other segments.
Ultra MegaMax Dominator 3D printer: [
drmrehorst.blogspot.com]