Not at all. It's whatever is right for the mum and baby. Some mum's want to breastfeed but really struggle with it (like my wife). Worked out quite nicely for me though. Same with my wife, albeit only with 2 kids. They only really need to breastfeed for the first week anyway, that's when the colostrum is coming through. After that it's very easily substituted by formula.
and you get the added bonus of being able to ascertain the exact centre of the Earth by following your nips.