I menu plan .
If I didn't we would waste loads of food. I agree that you tend to have a lot of "staples" e.g. rice, pasta, tinned tomatoes in the house anyway, and stuff like fish, chicken, mince etc in the freezer. But if I didn't menu plan, I wouldn't know what I needed in the way of fresh things like mushrooms, peppers, sping onions etc.
I plan a meal for each night, although sometimes the meals end up being swapped round within a week, e.g. we end up up having Monday's meal on Thursday and vice versa.
I do cook recipe type meals most nights, but they are often ones I have done frequently, so don't actually need to consult the recipe while cooking. If I want to try a new recipe, or something I haven't cooked for a while, then i try to do it on a day when I will have a bit more time.
I can't imagine going shopping and not actually knowing what I would need in terms of fresh ingredients.