Big pot, little pot
Anyone seeing my kitchen for the first time would probably be surprised at the number of pots and pans I have crammed onto my shelves (there are even more tucked away in the cabinets). I have sturdy, heavy black cast iron; colourful enamelled cast iron; a hand-pounded carbon-steel wok; a set of nesting Cristel pans with detachable handles, which makes them great for storing; and lots of beautiful stainless-steel-lined copper pans I bought on sale. They range in size from about 6cm across for a lovely copper pan with a capacity of about 200 grams, to an enormous Le Creuset that weighs about 9kg.
Do I need all of these pots and pans? Of course not; I've cooked in kitchens with a lot fewer. But having so many makes cooking much more pleasurable - because most of them are beautiful (especially the copper and enamelled cast-iron pans). And each has its own use. The tiny copper pan is perfect for melting butter. Yes, I could do it in a larger pan but it would scorch more easily because of the wider surface area. The next size up is used for making one or two perfectly boiled eggs; if you cook them in a pan that's too large, you need to add more water so the eggs are submerged, and it throws off the timing. I have one copper pan that I use for simmering milk and cream - it has a small lip, so when transferring the hot milk or cream from the pan, it pours evenly, rather than dribbling down the side.
I have certain pans for cooking for two to four people and others for making larger quantities of food. Copper is used for sautes while the enamelled cast iron is better for braises. You can't cook a lot of food in a pan that's too small - the ingredients won't heat evenly, and it might boil over; and if you try to cook a little in pans that are too large, the liquid will evaporate too quickly, scorching the food.
Pans that are taller than they are wide are good for boiling and poaching, while their counterparts are better for reducing liquids quickly. I love my ugly black cast-iron pans for frying, and because they've become so well seasoned over the years, I also use them as a griddle for making French toast.
Although my shelves are full, there are more pans I would love to add to my collection: one for making tarte Tatin, an unlined copper pan for preserves (because the metal conducts heat so quickly, it cooks the fruit faster so it keeps its fresh taste); and yet another unlined copper pot for caramels (the metal reacts positively with the sugar, lessening the chance that the sugar will crystallise). There's no space for them, though, so these purchases will have to wait.