Some people believe that it is ALL breast milk or none at all. But the truth is that even a small amount of breast milk a day has benefits.
This article explains that if you nurse your baby once and give formula bottles for the rest of the day, you are still giving your baby all of the wonderful benefits breast milk has to offer.
For the first 2 months of Joslyn's (my oldest daughter) life, we gave her one formula bottle a day. When she got that bottle I pumped so I was still keeping my supply up. With Katelyn, we tried formula once and she hated it so bad she refused to eat it. So we have not given her any more since. But we do have an emergency stash in the laundry room.
So I am not going to say that it is horrible to give your baby formula nor do I pass judgment. But I do feel any amount of breast milk is just such an amazing gift to give your babies and no one should feel guilty if they need to supplement with formula. But it is not for me to decide...... even though sometimes I wish I could!