You may miss out on significant savings through the use of store specials and coupons. These missed savings have a potential to add up, depending on how much food you are buying. At times, the savings from sales and coupons will make the trip valuable.
The online grocery stores are generally higher priced than conventional stores. Not only will you miss out on potential savings, but you will have to spend more for the convenience.
Many online grocery stores and delivery services will charge fees for the shipment and delivery on your items, regardless of how much you spend. This tacks on even more to the bill.
Often times, online grocery stores have a much more limited inventory than conventional stores, and their online inventories may not be correct all the time which means if you order an item, you may not receive it right away.
You will have to be sure you are at home during a certain time of the day when the groceries are delivered.