The only reason I can think of why they would want this, is if you filed and reported you had more than $9114 withheld in the box 4 total of your own W-2 forms from multiple employers.
You get a refund of the excess over $9114 in that situation, but occasionally, a married couple accidentally indicates both their W-2 forms are just for one of them, and claims an excess refund that is not appropriate.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
