Someone did sort of explain on the earlier threads.
It's a no-brainer.
You have to keep weight and BALANCE within the allowable range.
When single-pilot in a teeny chopper such as a Robbie (US counter-clockwise rotation) you are required to sit in on the right to stay in balance.
If the rotor goes the other way (clockwise, European) then you will probably have to sit on the left when alone in order to stay balanced.
D'oh.