French cuffs are considered to be more formal than button cuffs. Although more formal, French cuffs are optional and a matter of preference. If a standard suit (as opposed to a tuxedo) is formal enough for an occasion, then so are button cuffs. For an job interview in a business environment, shirts with button cuffs are generally prefered to those with French cuffs.
Alternatively, instead of cuff links, French cuffs can also be closed with the much less expensive, but just as formal and well-regarded, silk knots, sometimes called monkey's fists. Silk knots tend to be better known in Europe than in the United States.
