"No wonder the path of Qi Luck has such a large trade off, losing so much lifespan, yet so many people still engage in its cultivation. Aside from anything else, the speed of cultivation progress alone is worth the life lost."
Lu Yuan's understanding of the Qi Luck is similar to a time accelerator.
Your life is accelerated compared to others at the same moment. So during this acceleration, your cultivation progress is stronger than others, but equally, your lifespan is used up faster.
Therefore, for a cultivator, cultivation of Qi Luck is tantamount to shortening a task that would normally take hundreds of years to just a few years.
As for the pros and cons, it depends on individual needs.
As far as Lu Yuan is concerned, he quite likes this type of acceleration method.
After practicing for a day and a night, and accumulating enough mana to perform one-sixth of a spell, he ended the cultivation as the new day came.