This is actually quite common. If you use one saute/frying pan for "everything" and a particular batch has only a small amount of food in it, if you lay it flat then the food may cook way too quickly because it is spread out in a thin layer. Tilt it as shown in the picture and you have the equivalent of a much smaller pan with the food, and especially the liquid, much deeper. I have done this myself - too lazy to pull out another pot for a small batch. But for a professional chef it can make even more sense - switching pans constantly for different orders takes a lot of extra time.