Longer rods make it slightly easier to manually calibrate printer.
Numerical calibration of the printer will be more informed (chances of better convergence) when rods are shorter but still reach significantly behind the triangle connecting virtual tower positions.
Shorter rods (which can get almost horizontal) can lead to missing steps for firmwares which keep constant head speeds when a rod pair is getting almost horizontal. This is because the carriage speed needs to be much quicker than hotend speed in these cases.
Here is an example chart showing how much a carriage must be quicker than the hotend depending on the distance from the tower base:
The shorter the rods the more chart left/right sides are used ... and the right side is obviously dangerous.