I tried butts both ways. I prefer not to foil as I do not like the mushy bark. I sometimes inject the butts. Flavor wise, the injection helps get the flavor deep into the meat. Moisture wise, I do not find much difference. I feel butts have enough fat that it will help retain moisture.
Just my preference.
I do foil chuckies and briskets.
Bubba Keg / Stumps Baby / Super Fast Yellow Thermapen / Lodge Cast Iron Grill / Coon Ass Pizza Oven