as a general rule if a boat has been designed with a jib it should be basically balanced with both sails up, hopefully with a slight tendency to head up for safety reasons

sailing it without the jib will move the center of pressure of the sail behind the center of pressure of the hulls and increase the head up effect

a beginner skier thinks that un-waxed skis will be safer cause they are slower but as they are less controllable they are actually worse
in the same way on my nacra 5.2 i find soloing without the jib much more difficult as it is so much easier to go into irons. it's actually easier to sail uni with someone else on as the weight helps you coast through the tack