Which of the following is NOT a key point to determine if home-office expenses are deductible?

The deduction of home-office expenses is largely governed by specific criteria set by the IRS to ensure that the home office is primarily a legitimate business space rather than a mixed-use area. Among these criteria, the notion of exclusivity is paramount. The correct answer indicates that the usage of the office for personal activities is not a determining factor for deductibility, which underscores the requirement that the space must be used exclusively for business purposes.

When the office is used exclusively for business, it strengthens the case for claiming related expenses, as it delineates the space from any personal use, reinforcing its role as a business asset. The other points focus on the nature of the business activity occurring in that space: whether it is the principal place of business suggests that the home office is central to business operations, while convenience for the employer addresses whether the office setup serves the business's operational needs effectively.

Thus, understanding that personal activities have no place in the consideration for deducting home-office expenses highlights why the correct choice is indeed about personal use and its lack of relevance in determining deductibility.