In your case, assuming you took the standard mileage expense of $0.54 per mile, this would have lowered your business income by $8,584, which most likely had a significant impact on your tax return.  Since your husband is an employee, his business miles should be treated as an unreimbursed employee business expense, and as such only the employee business expenses above 2% of your adjusted gross income are added to your itemized deductions.  Depending on your AGI and other itemized deductions, there may be little or no tax benefit from his mileage.