The short forearm does allow use of a full-length sidesaddle.
It also allows easy access to the loading port with the action open. You can fully load a magazine and also drop a round into the ejection port. This way, you get full mag +1 in the shortest time possible and you're ready to fire as soon as you close the action.
The long forearm is easier if you have shorter arms or the length of pull is too long. If this is the case, I would humbly suggest a better solution might be a shorter stock.