Why do I need to choose a slot before I place my online groceries

Why do I need to choose a slot before I place my online groceries sainsburys book slot Sainsbury's has released the following Christmas delivery slot schedule but slots are not yet open to book, the supermarket are keeping this sainsburys book slot Sainsbury's has released the following Christmas delivery slot schedule but slots are not yet open to book, the supermarket are keeping this

sainsburys book slot TESCO and Sainsbury's have revealed the exact date shoppers can book their Christmas delivery slots for this year

sainsburys delivery slot book a food order on the SAINSBURYS website I get as far as The weird thing is I can book a Christmas slot or a savers slot, but TESCO and Sainsbury's have revealed the exact date shoppers can book their Christmas delivery slots for this year