As mentioned above, with roots as a foodstuff derived from a by product, something left over has turned into something that is saved and is even used to express something worthwhile or 'good enough to be turned into Tsukudani.'
上述のように余り物利用の保存用食品であったことから、物が有り余ってもて余すさまを「佃煮にするほど」などと表現したりする。