Here's something I learned this past weekend at Wanee. When you engage the hold button, it locks out all controls, including the gain knobs. When you disengage the hold, the gain will change to whatever setting the gain knobs are at that time. I had the hold engaged, levels began to run hot/over, I adjusted the gain knobs first, realized I needed to disengage the hold, and when I disengaged the hold I had horribly overcorrected the gain and my levels were now way too low. This resulted in an ugly swing in levels that I'll have to fix in post that could have been completely avoided.