On rare occasions I will hit a pretty bad patch of soil; usually fill dirt from some old industrial site. If the sensitivity is running at single digits in auto+3...... and the sensitivity number is staying pretty consistent..... then I will check the "enable GB" box, pump the coil, and perform an auto (it's not really manual) ground balance. 99% of the time however, I leave the GB box un-checked and let the CTX's ground tracking work its magic.