A further reason you might lower an implement that was left up for a long time, right before starting, would be that if it has drifted down, then as soon as the engine starts turning the lift mechanism would call for lifting action. That is, the control lever doesn't drift, only the implement. Thus at the moment of starting the control is demanding flow. This sounds like a bad idea, and at least would load down the starter motor and/or the engine whose oil has barely started flowing.
Just as a data point, I intentionally left my ballast box raised overnight, because I had filled it with concrete and used the top link and the adjustable lower link to get it nice and level so the concrete surface would be horizontal. Then I checked it first thing this morning. It had not drifted down any that I can tell. The tractor's quite new so seals should be their tightest. This was in a locked barn and was a special case, not a habit, just stating an observation here.