Hey, I just finished watching Sober live at Reading festival and I noticed that Adam's thumb position is all the way at the bottom of the guitar neck. Is there a name for this technique and are there benefits of playing this way? Thanks.
It doesn't really have a name because it's not something that 99.99999% of guitarists will ever do, and frankly most of the time when I've seen it, it's been compensating for a guitar that has awful upper fret access, like Adam Jones' les pauls. Personally it's not something I think you should seek to imitate as it only has benefits for guitars where you can't reach high up on the fretboard with your thumb on the back of the neck. Otherwise you lose fretting hand stability and probable some power as well.

The only other time I've seen someone do anything like that for another reason is the very few times I've seen Guthrie Govan use his thumb under the neck to fret some frankly ungodly chord shapes. Even that I've only seen I think twice ever; once on video (I think in a series of interviews with Michael Casswell) and once in real life.
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Zaphod_Beeblebr Yes, you are right. I have a les paul and i find myself wanting to bring my thumb down to reach the higher frets all the time. the upper fret access sucks on those but they sound so good!