reduces AGI. It is especially true now with the high standard deduction. My FIL does it every year after I told him about it, but it felt like I had to do a sales job to convince him. I will also do it once I turn 72 (RMD age just changed from 70.5 to 72 I think). I can't quickly think of an example why you wouldn't do that every year. Maybe the board can some up with some reasons why, because I can't think of any.
QDC's are always done out of a retirement account but you would NEVER want to use Roth money. Not sure what the OP means about brokerage account - I assume it means a brokerage IRA.