Per the original rules, each day of downtime you spend crafting only allows you to create a total value of 5gp. This means if you were to make a basic poison would cost you 20 full days of nothing but crafting and 50gp (because the crafting cost is half market value). With this feat, the ability to make poison is incredibly cheaper, and not to mention faster. You should also speak to your dungeon master about learning to craft more potent poisons as the game goes on.