Always best to ground balance when starting out, no matter what. Then recheck ground balance every now and then. It takes nothing to check and readjust if necessary. You want to maximize the machine potential. As you hunt and move around, the conditions will determine how often you need to readjust the ground balance. The more the conditions change, the more often you ground balance readjust. It takes nothing to pump the coil and check.
After awhile, a knob to adjust ground balance becomes habit and you will find yourself doing it and not really put much thought into it. I prefer a knob for ground balance rather than some pushbutton menu driven machine.
Having a machine with manual ground balance lets you adjust to conditions over a preset ground balanced machine. Most preset machines do a good job for many conditions, but the manual machine lets you adjust as conditions change.
I use both types of machines, but I really prefer manual ground balance. Alway adjust for the soil and not over a target.
To answer your question, if I go back to hunt the same ground from my last hunt and use the same manual ground balance machine, you bet I will ground balance to start, And as I hunt, I will pump the coil fairly often and adjust as necessary. Only takes a second to pump the coil and check. And if a minor adjustment is needed, it will only take you a few seconds more.
I will usually adjust also just a tad on the positive side. Easier to know if it gets pulled towards the null region.
Like I said, after awhile, as your going along, you'll just take a second to pump the coil and have your finger against the knob to make minor adjustment if necessary. Comes automatically habit and only takes a second or so - and you know your maximizing your machine capabilities to the soil conditions. I prefer it.