Why do we need to keep breast milk?

Going to be a first time mum. Breast milk storage bag was one of the 'must buy' item in my list. However husband say not necessary. His reason - I just need to breast feed each time baby is hungry. He say I need not keep my excess milk once baby had enough. He have seen lots of online mummies who kept bags & bags of breast milk in the freezer but end up they either give away or throw away. But no mama wants to dump away their precious breast milk. Any other reason why we keep breast milk? How can I explain to my husband the need to store breastmilk?