Everyone is basically correct...
My Long Answer:
That 'box' means "Enable
Manual Ground Balance" and "over-ride the detectors automatic ground compensation algorithms" and "now hand over all that responsibility to the operator."
If you check the box, that means you are now
required to do manual ground balancing properly...and frequently. (Frequently, because Manual GB doesn't 'track' or 'auto-trac'...and it drifts.)
It also means you accept the responsibility for doing what is normally the detectors job, and that you are certain you know better about adjusting for the ground than the detector can ever measure or do.
And If you do (manually balance properly/frequently), and do it right...UNDER THE PROPER CONDITIONS...it can help (some) with depth
in bad ground.
BUT...If you just check the box and just start hunting (without balancing properly/frequently), you're doing it wrong...that's not what it's for.
You're badly hurting depth, and you're throwing away targets every time you turn the detector on, because (remember) it saves all the setting, so it's still checked after a power cycle.
This may be a recurring question that keeps coming up...but, the answer has always been the same...
As stated many, many times: It's almost always better to leave it unchecked....especially if you're not absolutely certain what it does...and let the detector do it's job.
My Short Answer:
"If you have to ask, leave it alone and unchecked."
mike