Well the rational reason is so that huge DGS and DH won't eat everything before I get a chance.
All my storage boxes get appropriated by DGS when he is packing up his lunch for a day at work. Even writing 'Grandma' on them doesn't stop it. So I hide them.
But apart from that, don't you think it's kind of cosy to have secret food in pretty little containers hiding away that only you know about? Biscuits, chocolate, expensive tomatoes and apples, other little treats?
My mother used to do it with butter (during the war), chocolate wholemeal biscuits and tins of condensed milk.