[Chadd]

An aircraft never needs to be balance from side to side, though it may need to be balanced from front to to back if it is not full. As for the aircraft being too heavy, it could have been a couple different things. If a lot of bags were on board, it could have exceeded the maximum takeoff weight or the maximum gross weight. That isn't very common and likely was due to the aircraft carrying a full fuel load, in addition to a full load of passengers and bags.

Charter airlines are much more common in Europe than in the US. It's a tougher industry here, much more difficult to turn a profit.