How does one prove they don't use the room for anything else? Webcam recording throughout the month? Also, this kind of deduction favors the rich as the poor can't afford having one room just for that.
...and/or favours the educated: if you have to go to the bother of knowing about this allowance _and filing a tax return_ to claim. In Germany many (most?) employees pay their income taxes automagically via payroll deductions and so aren't required to submit an annual return.
It absolutely 100% favors the rich. As do most tax incentives.
Completely favors the middle class that can afford to keep one room for 'work'. One wonders if starving artists can get some tax returns for their attic shoebox ateliers.
A more fair options would be to still allow the room option for simplicity but also allow you to deduct things by the square foot so even if your office is just a corner it could count, though that is really mushy and people don't like mushy tax laws.