For peak performance you should always use a Ground Balance that is as close to "on-the-money" as possible IF you are searching in the All Metal mode. This way you'll be more responsive to subtle little changes, positive and negative, and Yes, you might get slightly better depth on some deeper targets ... IF hunting in the All Metal mode.
However, I've found that most Tesoro owners, as well as users of other brands, tend to search in the motion-based Discriminate mode. Then things start to change a bit and I've found that you will get the best depth of detection and overall performance if you have "Power Balanced" in the Discriminate mode. Some detectors, such as the White's Classic series, NEED to have a just very slightly positive GB in All Metal in order to function well. A "spot-on" GB in All Metal tends to be a bit too negative for the Disc. mode, especially in more moderate to highly mineralized soils.
With most Tesoro models I had/have you need to set the up with a slightly negative GB in the All Metal mode in order to be close to the best functional GB setting for the Discriminate mode. Thus, if you Power Balance in the Disc. mode, the result is a somewhat negative GB in All Metal. If the GB is set too positive, and ground mineralization might or might not have that much bearing on the Disc. mode performance, you can lose depth of detection and/or detection ability of larger and/or higher-conductive targets, such as silver quarters, silver halves and silver dollars.
Personally, I favor using any make or model that affords me the opportunity to manually adjust the ground balance in order to maintain an optimum setting. Usually, I adjust the GB to be "spot-on" in the All metal mode, but users of Tesoro models, know that this is not an easy task, especially in 'bad ground.' The GB adjustment, be it an internal trimmer or an external manual control, is all too often a bit 'touchy' and really more coarse than I would like to see. I wish the GB controls (external manual adjustments) had more 'fine-tuning" adjustment range than they do.
I just returned from vacation and had to explain manual GB to several people who had either an original Bandido or a Bandido II