I'm a 50-something and have been at it for 20yrs. Was told a long time ago not to touch the disc with my free hand on the reach back. Tried to avoid that little incidental contact for awhile but it felt too unnatural for me and I reverted to the touch. Can't say exactly what it did for me except that it was some kind of position feedback. I see a lot of players do it - at pro level, too.

Recently became aware that I was no longer touching the disc on hard, high anhyzers and was seeing an increase in power/distance on those shots, so I tried again to avoid that contact on the turn back on all drives. BIG increase in D.... Guessing I'm turning back further as my free hand was probably limiting that motion to a degree. I need to work on accuracy now but this is big, for me.

I use both hands when throwing for accuracy in the woods, but lose the extra hand when throwing more for distance.

the off hand has a direct corrolation with where you head is turned.
on short to middle distance when your looking at the target the physical position of you reach back is shorter therfore your off hand can reach the disc.
on greater power shots when your not looking at target during the entire throwing motion the off hand cant reach the disc at the furthest reach back because the torso turns the off shoulder away from the throwing shoulder.
a powerful full reach back is hindered dramatically by closing the chest to allow the off hand to reach the throwing hand.

Yup.. Making sense.