In industries with billable hours, productivity is not particularly easy to measure and an hour billed from home looks just fine on paper. To managers, that is an hour on a spreadsheet with somebody else paying for the coffee, lights, heat, insurance, cleaning (or just not cleaning), etc. But there are some studies from industries where productivity is more measurable. Results are all over the place, but this particular study from Japan puts working from home at about a 30% productivity loss compared to the office. Something in the range of a 20-50% loss seems to be a common assumption from a range of studies.