I guess you’re referring to the “famous” 4 physical fields/day “rule”? From the FAQs:
So it’s up to you and what you feel you can handle. With face/skin fields, most people here seem to use them within stacks made of several fields (more than 4) that work synergistically. So do I. And if I remember correctly, SilverZuzu for example had a beauty stack she was using on specific days of the week for maintenance purpose.