One of the more significant expenses for the small business owners is income taxes. Since most small businesses are tax pass through entities, it is beneficial to the business to have the least amount of net income in order to reduce the tax obligations of the owner(s). This is achieved by making sure every dollar expensed is deductible for tax purposes.
Personal expenses are generally considered non-deductible no differently than on your personal return. The key is that sometimes these expenses are marginally used for the business operation and therefore a reasonable individual would conclude that they should be deductible for the business.