There is a limitation related to home office expenses and the income that was earned while using the home office. This question is gathering information to apply that limitation.
The question is asking what percentage of your business gross income is attributed to work
done in your home office.
For example: If all your work is done in your home office, enter 100 (for 100%). But if you figure that one-fourth of your income is made on the road or in another location and three-fourths of your income is made from your home office, enter 75 (for 75%).
You can also consider the amount of time you work in your office as a factor if breaking it down by income is difficult. If you spend 4 out of 5 days working from your home office, then use 80 (for 80%), etc.