It's really dry here. Even with powdered, we never get clumping.
I use granulated when the SPOG will be moist during the cooking, and sort of "stew" while cooking.
But for situations where the flavors need to be better dispersed, or things are dry, I use powder to get a more even distribution earlier on.
An example is when smoking pecans. I use powdered onion and powdered garlic because it will be applied, along with melted butter, to the nuts prior to smoking.
In that situation, granulated garlic or onion would not adhere well, and would result in chunks where it does stick.