Just because you have a luggage allowance of two suitcases up to 30kg each does not mean you should use this allowance in full, unless of course you are relocating somewhere for a long time or returning home after an extended stay abroad. I know this because four suitcases are a right pain to lug into a fourth floor Parisian walk-up. It also becomes difficult to find vehicular transport between accommodation and airport. Utilisation of the full luggage allowance may cause you to end up wedged behind a ping-pong table (still in box) in the back seat of a relative’s car. This could prevent you from seeing the sights of Edinburgh, or any other city.
Furthermore, you look like a goose and people will laugh at you. There are never that many contingency-requiring events, unless your journey involves a base camp and walking up a mountain in Nepal.