I would guess that if you use the space less, you use less light, heat, cooling, water, or whatever costs are associated with it. ? But I want to know this, too. I do not have this deduction, but I always thought the home office deduction was relevant if you had a demonstrably appropriate separate space and could calculate its size and percentage or portion of utility and other costs.
My garden in England is full of eating-out places, for heat waves, warm September evenings, or lunch on a chilly Christmas morning. (Mary Quant)