For utility bowls, I won't take a core less than 8 inch diameter and 3 inch deep. Too much work, and not enough return, plus I end up with a lot of very small bowls that sit around. For the Mahoney type stacked sets, he goes down to tiny 2 inch diameter pieces some times, but these are high priced burl pieces and you want to use every scrap. So, I guess the answer is 'it depends'. You can turn a cylinder and part off plate blanks, or shallow platter blanks, but I find it easier, or maybe more efficient to cut the pieces out from stock. Having a bandsaw that cuts 16 inches high really helps that part.
robo hippy