This is a great question. To me it comes down to quickly counting stacks in no limit. And to me fewer denominations is easier to count than fewer chips.
So ideally a nl stack contains mostly the workhorse chip and then a handful of blind chips. Two denominations only is easy to count. Three denominations is okay, but if you get to four denominations it can get challenging to do in your head.
Bottom line, I can count 42 reds, 5 blues, and 7 quarters in my head faster than 3 greens, 26 reds, 9 blues, and 11 quarters, even though both total $216.75. (though I can do both in my head.)