Business expenses that can be written off have an important role to play in keeping your business profitable. They can help you save money on taxes and increase the return on your investments. Here’s a quick definition of what business expenses can be written off: Business expenses are expenses incurred in running or managing a business, such as equipment costs, advertising, insurance, wages and salaries. These expenses must directly relate to the production of income or the operation of a business; they must also be ordinary and necessary expenses within the industry. By writing off these kinds of expenses, businesses can reduce their taxable income.