The IRS doesn't care what you claim on your W-4. Besides, they never see the W-4. The IRS only cares what you claim on your tax return when you file it, and that you pay your taxes if owed, at the time you file your tax return.
Most couples, if their only source of income is W-2 income, will claim on the W-4 at least 1 less than they are entitled to. This increases their withholding from each paycheck. That way, they are practically guaranteed a refund when they file at tax time.
If enough taxes are not withheld from each paycheck, it could result in you owing at tax time. If the amount you owe is substantial, then the IRS will assess an underpayment penalty for not having enough withheld from your paycheck throughout the year.
