Some perishables like fruits and vegetables are terrible to buy. Cilantro comes in a massive bunch from which I take three sprigs, and its rotten in a couple days. Bananas are unedible until day 2, then I have maybe a 3-day window to eat all the bananas before they are flabby, brown, and mushy. Even if I throw a handful of arugula in every single one of my meals, its massive tub is barely half empty by the time it starts rotting in my fridge a week after purchase.
Even if I plot and plan to use all my cilantro in 3 days, all my arugula in 1 week, power through 3 bananas a day during my bunch's window of opportunity, I can still end up going out for dinner which throws everything out of schedule. Or maybe I forgot to pull out the chicken out of the freezer and into the marinade this morning, so there is now no point in cooking if I need to wait 2+ hours after I get home for my bird to thaw and flavor.