Fatigue is a mechanic that forces you to think and prioritize what you want to do that day.
It is a bit subtle, but the game make it so that your/Karryn's daily choices matter and got to live with the consequences/find a way to overcome it. (Okay, not that really subtle with the forced auto-save)
For example, it was really hard for me to do the waitress side job while I was grinding the urinal passives.
So I made a choice to stop Karryn's urinal duty for a day to get a good night rest and restore her charm stat back to normal, which enables me to readjust her accessories to better cope with both (+ the receptionist side job).