What is so terribly game breaking about warforged not eating/sleeping/breathing?

They miss out on spending a few gp a week to buy supplies. So what?

They get to guard the group every night. It's not like a smart group won't just have shifts anyway. Most warforged are actually pretty bad at guarding. -2 Wisdom= bad spot checks

Being able to breath underwater seems like it'd be a cool advantage but then you forget heavy warforged sink like stones and are still vulnerable to pressure damage. Not to mention they can't fight well if they have the wrong weapons.