Back in my younger days I had caused smoke bitterness in food when using way too much in a short period of time, clouds of it. I was also using wet hickory wood chips at the time and the combination was way overboard. I think by using good aged wood, or the AMNPS you get a better quality of dry smoke at a low rate per hour, the old TBS.
While I only smoke a butts for 3 hours, it's only because we like less smoke flavor and my wood chunks from last falls cuttings are not fully cured yet. They put out a fair amount of smoke even when wrapped in aluminum foil with a few small holes.
My assumption then is that a small amount of smoke over a long period of time is fine and much better than moderate or heavy smoke over a short period of time.