The Compadre runs in full sensitivity all the time. Machines with a sensitivity adjustment can be turned up or down (usually down) for conditions that warrant it, such as reducing the sensitivity when encountering high mineralization, electrical interference or hunting close to an iron fence etc..
Threshold is NOT about the same as ground balance. The Threshold hum serves as a background sound level to enable one to hear slight variations in signal (deep and/or small targets) when in all metal mode that are not strong enough to be heard when in discrimination mode.
Ground balance is the adjustment of the machine that lets it ignore the minerals in the ground. Where mineralization is a factor, proper ground balance can increase the depth and sensitivity of the detector. The Compadre, Silver umax, Cibola and many other Tesoros have a factory preset ground balance that can't be changed without opening the box. They're set to what is (hopefully) a workable average that serves quite well in most areas. The Lobo Super Trac (in all metal) and many competitors machines now have a true automatic ground balance that adjusts as the coil goes over different areas.
The Vaquero with the manual ground balance has the edge over the Cibola because it can be easily adjusted to the changing mineralization from one area to another - for instance mild farm soil to rocky, mineralized mountain areas. Preset machines can and do work well in many locations, but manual or auto ground balancing enhances the usability of the machine in difficult ground. For most of the hunting I do the presets work pretty well and i've found a lot of goodies, but I do have one machine with manual GB and one with Auto. for the times I may need that feature. The thing is, manual or auto ground balance never hurts as long as the setting is correct, even in the milder ground. .
Hope this helps,
HH
BB