Other advantages to be had with manual GB, you can offset it to run a little hot, you can adjust it to clean up a scratchy signal, i can adjust it on my detector to miss small targets and just detect large items or vise versa, you can balance out hot rocks, coke etc
Some detectors are more ground reactive than others, some you can run well off balance with little depth effect, some need it perfect to give accurate screen ID's, some need constant adjustment as you hunt.