GP Extreme settings

Here's a question that has been buggin me since a trip to Laverton last year. Prior to the trip, I watched a vid clip from a so called minelab expert. It's no one from this forum or the other well known forum and I won't say who it is, but they are well known.
The expert suggested, unless you are in heavily mineralised ground, turn the "signal" dial completely off. So I did.
I was still able to detect targets buried up to at least 6 to 8 inches. I have posted the pic on this forum of what we found, junk I know but we still found it buried to a good decent depth. The only area I couldn't detect was heavy ironstone (I didn't think to turn the bloody dial up).
So my question is, why is it suggested to have the "signal" dial up to at least 75% or more, if the ground is not heavy mineralised or does it have a lot to do with the coils I was using (coiltek 14x9 ellip mono and sometimes the 16" round mono).

I use my signal as a fine tune threshold if you want to call it that.. Dial it down when it gets too hot, and crank it up when the ground is not as hot.
I just wind mine up till it becomes unstable or warbles or chatters. and knock it back a bit...
I have noticed that i really needed to keep dropping my test piece when i played around with the signal settings, and threshold...
I drop it GB near it, and see if it still stands out..
Sometimes i was GB over it, so had to finetune the signal a little..
Probably a different story with tracking, but i never use it ever. Dont like it and dont trust it even on the 5k.

Fighting hot ground was the only reason i upgraded to the 5k, and i still trust and love the extreme for its ease of use..
You dont have a lcd to look at, just dials to spin,buttons to flick and once u know where they are u never even look at the control box to switch anything over.
Th only mod i should have made to the extreme was a GB button on the handle, I think it would have made life much easier, and out of laziness the lack of GB make u walk over nuggets and miss em...

Was signal also connected to descrim in descrim mode? Or something like that? not that i ever use that mode...
But one button had 2 uses when it was in another mode..

I've never used the descrim yet (I dig everything) , and using a mono coil cancels out the descrim on an Extreme anyway. This was a one time only (trial if ya like) where I had the signal dial turned off but still found targets. I'm sure I was missing the small stuff, it was only finding big hits.
I do switch now and again from fixed to track and sensitive/normal, shallow/deep/normal on the area I have just gone over. Ya gotta try everything.
The machine is bloody excellent but does get lazy so I throw the pick at it to waken it up. I'm starting to think, it comes down to the ground ya walking.
I think I gotta get back to the Laverton area I was in and try with the signal on all the way.

I could never put up with the chatter in shallow mode, but thats one thing i really wanted to try out on the small stuff