There are risks associated with feeding during shed cycles. Although not common it can and has happened, the prey item after ingestion is not as flexible as the rest of the snake. The skin being shed is not as flexible as the new skin (why it sometimes looks wrinkly during the shed process) the partially digested rat can pose a 'road block' and the skin during shed can get trapped at or above the rat in the snake. The snake may not be able to get the shed over the thicker area, shed shrink as they dry out (measure a fresh one and then again dry) this shrinkage compresses above the stomach that is likely to cause stress at the very least perhaps need intervention and at the worst restrict blood flow from the heart to lower body, that would be bad.

The benefits of one or two meals are minimal and any risk no matter how remote over shadows the benefit seen by a meal or two. If the animal was small and suffered lots of weight loss it might be different but in a normal health animal a missed or postponed meal will make no difference so any risk is unacceptable to me.