Picking the right size pan for the job makes all the difference. Too big and sauces will cook down too fast or burn. Too small and dinner bubbles over on to the bottom of the oven.
Recipes often specify the size of the pot or pan, in quarts or inches. Too often we busy cooks will muble "Close enough," grab a pot, and keep going. We can't always be bothered to shop chopping and stirring to measure pan. (And we don't always own just the right size pan for the job.)
We're feeling pretty silly about now. We first found this "12 inches" mark on the bottom of a Martha Stewart Everyday skillet a few weeks back, while measuring it with a ruler to make sure it wasn't too big for the pork chop recipe. Now we're noticing numbers and marks on other pots and pans.
There's a number on the bottom of most Le Creuset Dutch ovens ...
This number refers to the diameter of the pan in centimeters, as we learned from 
Some of my Le Creuset pots are over 30 years old and can't believe I never made the connection from number to centimeters. Yes, I'm American, but my job required me to work in metric measures--duh.
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Also, most recipes I see specify small/med/large pots. I never am sure what they mean and just go by my instincts. Of course, sometimes that means I dirty two pots because I misjudge and run out of room.
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