the problem that isn't mentioned by its advocates is that you're not getting an 80% increase in output. you might not be getting a 40% increase in output. as a result, your overall productivity *drops*, because the amount of work you get done doesn't keep up with the time you spend at it.
if this is the case, why has it become increasingly popular in the land of the godmakers? because it's an effective form of social control among high-exit high-income workers. it signals a willingness to subordinate oneself to a higher goal. I'm not exaggerating. they'll tell you this.
the most malignant form of repression is the one that convinces you to inflict it on yourself. happy Labor Day.