I have found 0% to be much more stable accelerating out of corners - for whatever reason! Default/mid settings left me needing to be very cautious with my right foot (finger)!
My favourite settings so far:
LS Accel: 10 I want to see how high I can go on this without inducing power oversteer.
LS Decel: 50 I find lowering this too much leads to the back end stepping out while trail braking.
LS Preload: 120 Again lowering this too much leads to the back end stepping out in fast neutral balance corners.
I think the in-game comments on the LSD are half right, but on some cars having the diff lock too aggressively means the inside wheel (locked with the outside wheel) over-rotates, reducing rear grip and giving power oversteer.
Having a fully open diff allows the inside wheel to rotate independently and allows an easier corner exit on the power, but I do notice on 0% that you get some swinging engine revs getting back on full power too early.