When you cook from scratch you stock your pantry with ingredients not "food items" (prepackaged food mixes and such). The same ingredients can be combined in multiple ways to make many different kinds of food.
Knowing what ingredients you use on a regular basis means that it is easy to watch for sales on these staples and stock up when you see a good price. Knowing what ingredients you use often also means that you can shop in bulk for some of those ingredients. You can often get better prices buying in bulk than you can from watching for sales...and then no need to watch for sales, just buy in bulk when you need to restock!
Buying in bulk means always having ingredients on hand to make many of your families favorite dishes. It means less time grocery shopping. It means always having food on hand in case of emergencies...we may not like eating rice and beans for three meals each day, but I know that we have enough rice and beans on hand (plus other things) to keep us fed for quite some time.
Cooking from scratch and buying in bulk means that we are always ready to welcome guests into our home for a meal...just make a quick batch of biscuits, defrost some more cooked chicken, make some more rice, cut up another apple.
We grocery shop about once each week...a trip for fresh produce, dairy and whatever bulk purchase(s) is running low. Under an hour from van-to-store-to-checkout-to-van. Which is pretty amazing considering how long it seems to take us to get three kids into and out of car seats!