The only time I've noticed a difference on any Garrett machine is if it had a non-motion all metal mode. I have never found any difference in depth, even when I turned the threshhold down LOWER. Maybe I've not owned enough of their machines-about 20.
The very deepest of items cannot "punch" past a threshold that is set to be silent. When targets are trying to come through, but are too weak to trigger a solid audio response, the best they can do is upset the threshold.
Thats why those who want to find the deepest targets listen to the threshold.
On the Garrets, this upset sounds like a fleeting all metal tone, sort of a "burp" in the threshold. You often wonder if you really heard it. It will force you to whip your coil over the sound to try and strengthen it a little. But there isnt likely to be any cursor pointing at "quarter," or any audio "boooiiing!" to go by.
It will just be that whisp of all metal "something."
In tot lots and shallow modern sites, it may not be a big deal. But out in the woods or fields, it can make or break you. It isn't a depth function - that is set by your gain control (sensitivity). It is really an audio indicator of weak signals that you might otherwise miss.
I suggets you listen to Garrett and follow their instructions when setting the Threshold.
Repeat after me: "The Buzz is Your Friend.... The Buzz is Your Friend"