How much to actually store?

I’m 4 weeks pp and looking for a freezer because I’m pumping about 30 oz a day. My mom told me to freeze it all, but I’m kind of confused on why? My baby is exclusively breastfeeding we aren’t actually using the milk yet. I also dont know how big of a freezer to get because yes we could just get one that’s big enough for a year (30x365) but again won’t I never use nearly that much if I’m also breastfeeding? We just don’t have room for a large freezer so I’m trying to get some more info. Thank you!