I just finished a quilt that had larger borders on the top and bottom, and it looks fine. It needed to fit a twin bed, and it just wasn't long enough. This isn't the first time I have done it. Usually it is to make the quilt look better on a bed.
I am attaching a picture. It is a quilt for a boy at a Boys' Ranch, and it just wasn't quite long enough. The top and bottom borders are two inches wider than the side borders.
Dina