Tricky question and answer, the answer being largely dependent on the machine being used and where you're hunting? Take my Excal, for example, it has auto ground balance but even so threshold stability can still play a big part in all of this, as can machine sensitivity, etc. Per example, in some areas I hunt I have to sacrifice sensitivity in order to maintain stable threshold because if this threshold is unstable then so is everything else. Even when hunting in silent mode I'm still conscious of this, frequently turning up my threshold volume and checking the stability of my threshold whenever I feel the machine isn't performing as well I'd like it to. So regardless if using manual or auto ground balance there are still other factors that can effect things.